聚合物/层状硅酸盐纳米复合材料的环境稳定性

过去的十多年里，聚合物／层状硅酸盐纳米复合材料在制备、结构与性能方面的研究取得了长足的进步。一些聚合物基的纳米复合材料已实现工业生产，在汽车、家电和包装等领域得到应用。环境稳定性是聚合物材料应用的一个重要方面。本文从材料的耐候性、耐热性和阻燃性能的角度出发，评述了近年来聚合物／层状硅酸盐纳米复合材料在紫外光降解、热降解和燃烧性能方面的研究进展，以期对纳米复合材料的基础研究及应用开发有所裨益。     

THERMAL DECOMPOSITION AND FLAMMABILITY OF ACRYLONITRILE-BUTADIENE-STYRENE/MULTI-WALLED CARBON NANOTUBES COMPOSITES

Thermal and flammability properties of acrylonitrile-butadiene-styrene copolymer (ABS) with the addition of multi-walled carbon nanotubes (MWNTs) were studied.ABS/MWNTs composites were prepared via melt blending with the MWNTs content varied from 0.2% to 4.0% by mass.Thermogravimetry results showed that the addition of MWNTs accelerated the degradation of ABS during the whole process under air atmosphere,and both onset and maximum degradation temperature were lower than those of pure ABS.The destabilizat...     

The effect of AlBr<Subscript>3</Subscript> additive on the thermal degradation of PMMA A study using TG-DTA-DTG,IR and PY-GC-MS techniques

The thermal behavior of poly(methyl methacrylate) (PMMA) was studied in the presence of AlBr₃ using TG-DTA-DTG, IR and Py-GC-MS techniques. Degradation products were identified. It was found that PMMA started degrading at a lower temperature due to the generation of free radicals (Br^•), being the product of decomposition of AlBr₃. Despite early destabilization of the system, stabilization zone was also highlighted. Flammability test was conducted to check the affectivity of AlBr₃. Degradation mechanism has been proposed. Pyrolysis of the system (PMMA–AlBr₃) was also monitored by heating it at different temperatures.     

Inert effects on the flammability characteristics of methanol by nitrogen or carbon dioxide

Knowledge of material safety properties is critical for safe handing in the chemical process industries, especially for flammable chemicals that might result in serious fires and explosions. This study investigated the flammability characteristics of methanol under working conditions during the process. The targeted fire and explosion properties, like explosion limits (UEL and LEL), vapor deflagration index (K _g), maximum explosion pressure (P _max), and maximum explosion pressure rise [(dP dt ⁻¹)_max], were deliberately obtained via a 20-L-Apparatus in 101 kPa (i.e., 760 mmHg/1 atm), 150 and 200 °C, along with various experimental arrangements containing nitrogen (N₂) or carbon dioxide (CO₂) as inert component. Particularly, this study discussed and elucidated the inert influence on the above safety-related parameters by two different inerting gases of N₂ and CO₂. The results indicated that adding an inert component to fuel–inert gas mixtures determined the decrease of explosion range and flammability hazard degree. The results also demonstrated that CO₂ possessed higher inerting capability than N₂ in this study.     

Thermal stability and flame retardancy of polyester fabrics sol–gel treated in the presence of boehmite nanoparticles

Polyester fabrics have been treated with hybrid organic-inorganic sols containing aluminium hydroxide, namely a synthetic boehmite. The treated fabrics have been thoroughly investigated by infrared spectroscopy, scanning electron microscopy coupled to elemental analysis and thermogravimetry. Furthermore, the flammability of the coated fabrics has been assessed and compared with that achieved by applying the two components separately. More specifically, flammability tests have shown that the sol–gel treatment in the presence of boehmite nanoparticles is able to suppress the dripping phenomenon, which represents the main issue to fulfil for polyester fabrics.     

Novel nanocomposite based on EVA/PHBV/[60]Fullerene with improved thermal properties

A novel nanocomposite was prepared from ethylene-co-vinyl acetate copolymer (EVA) and poly-3-hydroxy butyrate-co-valerate (PHBV) in combination with small amounts of [60]Fullerene (C₆₀). The thermal degradation as well as the incorporation effect of C₆₀ on the thermo-oxidative decomposition of EVA/PHBV/C₆₀ nanocomposites was investigated using thermogravimetric analysis (TGA). In order to assess the level of stabilization of nanocomposites, the oxidation induction time test was also determined. The obtained results indicated that the dispersion of C₆₀ even at low loading (0.3, 0.5 and 0.7 wt.%) exerts a significant increase on the thermal stability properties of nanocomposite. The oxidation induction time values of nanocomposites were remarkably increased with the increase of C₆₀ amounts. Surprisingly, the oxidation induction time of EVA/PHBV/C₆₀ (0.3 wt.%) is 1643 s higher than that of unfilled EVA/PHBV blend.The flammability properties investigated in pyrolysis combustion flow calorimetry (PCFC) showed that the addition of C₆₀ could prolong the time to peak of Heat Release Rate (pHRR) of around 30 °C compared to EVA/PHBV blend. It was demonstrated that C₆₀ is inhibitor of the thermal and thermo-oxidative degradation of EVA/PHBV blend.     

Flammability, degradation and structural characterization of fibre-forming polypropylene containing nanoclay-flame retardant combinations

We have shown previously that the introduction of nanoclays can reduce the flammability of synthetic fibre-forming polymers like polyamides 6 and 6.6 only if used in conjunction with conventional flame retardants. In this work we report initial studies of the effects of dispersed nanoclays with low concentrations of selected flame retardants introduced into polypropylene on flammability, thermal degradation and X-ray diffraction behaviours. Flame retardants used include ammonium polyphosphate as a conventional char-former and a hindered amine stabiliser known to have flame retarding characteristics in polypropylene.     

Flammability, structure and mechanical properties of PP/OMMT nanocomposites

Polypropylene/organoclay (PP/OMMT) nanocomposites were prepared in a twin-screw corotating extruder using two methods. The first method was the dilution of commercial (PP/50% Nanofil SE3000) masterbatch in PP (or PP with commercial flame retardant). The second method consists of two stages was the extrusion of maleic anhydride grafted polypropylene (PP-g-MAH) with commercially available organobentonite masterbatch in first stage and dilution of the masterbatch in PP (or PP with commercial flame retardant) in second stage. XRD results showed no intercalation in composites obtained from commercial masterbatch without compatibilizer and semi - delamination for compatibilized systems. Tensile tests revealed that nanocomposites with 5% of organoclay have a slightly higher tensile modulus and tensile strength than pristine PP, however addition of the commercial flame retardant (FR) reduces mechanical parameters to roughly the level of those for neat PP. PP/OMMT composites have approx. 25% higher oxygen index than pristine PP, and this changes slightly after the addition of FR. The cone calorimeter tests showed a decrease of a heat release rate (HRR) and a mass loss rate (MLR) after the addition of FR.     

Study of flammability and thermal properties of high-impact polystyrene nanocomposites

To increase thermal stability and flammability of high-impact polystyrene (HIPS) nanocomposites with silica nanoparticles and two types of polyphosphate flame retardants were prepared by extrusion. Nanocomposites were characterized by thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, limiting oxygen index (LOI) analysis and the evaluation of mechanical properties. It was found that organic polyphosphate in combination with silica increased thermal stability and fire retardancy by 50% in LOI test. Morphology characterization revealed existence of crystalline order which affected mechanical properties; tensile strength was approximately the same as virgin HIPS while elasticity was sharply decreased. Ammonium polyphosphate did not affect mechanical properties as much as the organic material but was not equally efficient in flame retardancy which was just marginally increased.     

Flammability limits of refrigerant mixtures with 1,1,2,2-tetrafluoroethane

Extensive measurements have been made on the flammability limits of two binary mixtures of propane/1,1,2,2-tetrafluoroethane and 1,1-difluoroethane/1,1,2,2-tetrafluoroethane as per the Chinese National Standard GB/T 12474-90. Experimental data for the 1,1,2,2-tetrafluoroethane mixtures were obtained with estimated uncertainties of 0.09 mol% for lower flammability limits and 0.14 mol% for upper flammability limits. All measurements were carried out at atmospheric pressure and room temperatures around 20 °C. It has been found that molar fractions of propane and 1,1-difluoroethane in lower limit mixture decrease when 1,1,2,2-tetrafluoroethane, being itself nonflammable, is added to the mixture. Modification was made to the extended Le Chatelier’s formula for interpreting the dilution effect of 1,1,2,2-tetrafluoroethane. It has been found that the extended Le Chatelier’s formula using an individual set of parameters can fit the experimental results for flammability limits of propane and 1,1-difluoroethane diluted with 1,1,2,2-tetrafluoroethane well.