Three systems of FR treatments of polyamide 6 with conventional flame retarding additives in the absence and in the presence of nanoparticles are discussed: I. ammonium sulfamate (AS) and dipentaerythritol (Di) II. melamine cyanurate (MC) III. pentabromobenzyl acrylate in the monomeric (PMA) and the polymeric (PPA) form. Depending on the concentration of the nanoparticles; synergism, antagonism, and cooperation in flame retardancy as well as in mechanical properties are observed. Cooperation between the OMMT in the concentration range of 0.5-1.0 wt% and the FR in all three systems is observed. The decrease in PHRR (ΔPHRR) is different for the three systems. In system III the brominated FR behaves similarly to OMMT with respect to ΔPHRR. The interaction between the molten polymeric matrix and the nanoparticles increases the viscosity in all three systems, which slows down the supply of the flame retarding moieties to the flame and lowers the FR rating, as measured by the UL-94 and OI tests. A new approach for assessing the viscosity of the pyrolyzing nanocomposite is presented by determining the size and mass of the drops formed during the UL-94 test. Dispersion of the nanoparticles in the polymer decreases the HRR and MRR and decreases the UL-94, OI ratings, and the mechanical properties, as evidenced by the different behavior of OMMT and Na+MMT. The time of ignition decreases markedly by the addition of the nanoparticles, due to the low thermal conductivity and heat transfer of the protective barrier on the surface of the pyrolyzing nanocomposite in the pre-ignition phase. A possibility of restoring the high FR rating in the presence of higher concentrations of nanoparticles is indicated. The significance of the results obtained for the future of the use of nanoparticles in FR is discussed. 相似文献
Polyaniline/Na+‐montmorillonite (Na+‐MMT) nanocomposites synthesized by in‐situ intercalative polymerization of aniline into Na+‐MMT are reported. The expansion distribution of basal spacing of the silicate layers upon the increase of the amount of aniline relative to Na+‐MMT is, for the first time, estimated from the square of the full‐width at half‐maximum (FWHM2) of XRD patterns. According to the FT‐IR frequency shift of the C‐N stretching vibration, the change in the basal spacing of the silicate layers is closely related to the degree of hydrogen bonding between polyaniline and the silicate basal surface in a confined geometry. 相似文献
The microstructure, electrical conductivity and rheological properties of a nematic liquid crystal (5CB) doped at concentrations up to 4.5 wt% of montmorillonite (MMT) or organomontmorillonite (OMMT) clay nanoplatelets, were investigated at temperatures between 293 and 310 K. Microscopy and electrical conductivity assessment revealed noticeable differences in aggregation in MMT and OMMT suspensions, MMT nanoplatelets showing a strong tendency to aggregation. The incubation of 5CB in the presence of MMT initially produced loose aggregation, followed by the formation of compact aggregates. The latter had practically no influence on the surrounding inter-aggregate regions. In the case of OMMT, a greater degree of integration of the nanoplatelets was observed within the liquid crystal structure of 5CB, resulting in a noticeable effect on electrical conductivity and activation energy of the composite material. Thixotropy was observed in suspensions of 5CB composites formed with either MMT or OMMT. A composite of 5CB with OMMT also exhibited anomalous viscous thinning at shear rates below 100 s?1. A structural model is suggested to explain this behaviour. 相似文献
Gelatin/sodium montmorillonite (Na+MMT) hybrid nanocomposite films were prepared by a new photocrosslinking method using 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone (Irgacure 2959) as a photoactive radical initiator and N,N′-Methylenebisacrylamide (MBA) as a crosslinking agent. The prepared samples were characterized by X-ray diffraction (XRD), differential scanning calorimetry, stress–strain measurements and UV–Vis spectrophotometry. XRD patterns showed the formation of exfoliation structure resulting in considerable improves in mechanical properties of the nanocomposite. Retaining of transparency also suggested that Na+MMT nanosheets were uniformly distributed in the gelatin matrix. The tensile strength and Elastic’s modulus of nanocomposites were also improved notably by enhancing amount of Na+MMT. Furthermore, gelatin/Na+MMT nanocomposites showed a second Tg at a higher temperature in presence of Na+MMT. 相似文献
The poly(lactic acid) (PLA)/montmorillonite (MMT) composites were prepared by melt blending in an internal mixer. The effect of MMT and organically modified MMT (OMMT) addition on crystallization and mechanical preferences has been studied. The DSC results show that the crystallization ability of PLA is improved by MMT or OMMT. The addition of MMT and OMMT increase the crystallinity of PLA from 27.3 to 32.8%, and the cold crystallization temperature (TCC) of PLA decreases from 93.1 to 88.9°C with the MMT. However, the nucleating effect of MMT is better than that of OMMT due to the velvety surface resulted from the organic modification. The average size of the spherulites in PLA/MMT is smaller than that in PLA/OMMT. The addition of MMT or OMMT increases the tensile strength of PLA from 29.6 to 34.7 MPa and decrease the elongation at break of PLA. The modulus of PLA composites is enhanced rapidly from 338 to 660 MPa by the addition of MMT. 相似文献
The polypropylene (PP)/polystyrene (PS)/montmorillonite (MMT) blends were prepared by an innovative eccentric rotor extruder based on continuous elongational flow. Addition of MMT nanoparticles was found to reduce the PS droplet size and improve the compatibility of PP/PS. The MMT nanoparticles had clear intercalation and/or exfoliation structures and were located mostly at the interface of PP/PS. It was found that the intercalation and exfoliation of MMT was finished under the synergy of interfacial interaction and tensile deformation so that we called the mechanism as “MMT exfoliation mechanism induced by synergy of interface and tensile deformation”. The rheological analysis showed that incorporation of MMT led to an increase in complex viscosity to an optimum level (5 wt%), after which any further increase in MMT concentration decreased the complex viscosity. Moreover, the degree of crystallinity of blends was controlled by the heterogeneous nucleation effect of MMT and the inhibition effect of PS. 相似文献
Polystyrene (PS)/clay nanocomposites were synthesized by the emulsion polymerization of styrene in the presence of sodium ion‐exchanged montmorillonite (Na+‐MMT), demonstrating that the strongly hydrophobic PS was intercalated into the hydrophilic silicate layers. The nanocomposites were examined by means of X‐ray diffraction, transmission electron microscopy, thermogravimetric analysis. The rheological properties of the PS/Na+‐MMT nanocomposites were also studied to exhibit more pronounced shear thinning behavior with increasing clay content. 相似文献
Summary: Nylon‐6/Na+‐montmorillonite (MMT) nanocomposites (NNNs) are synthesized by a hydrolyzed ring‐opening polymerization. At a loading of only 2 wt.‐% MMT, the tensile modulus, the flexural modulus, and the heat distortion temperature of the NNNs exhibit increases of nearly 20%, 60%, and 63 °C, respectively. Compared with that of neat nylon‐6, the temperature of the main α‐relaxation (Tα) of the NNNs is shifted 3.6 °C toward higher temperatures and two β‐relaxation peaks are observed. Another interesting phenomenon is that there is a new melting peak (at about 206 °C) for the NNNs.
DSC second heating curves of neat nylon‐6 (N6), nylon‐6/Na+‐MMT nanocomposites with highly swollen Na+‐MMT (NHM), and nylon‐6/Na+‐MMT nanocomposites with slightly swollen Na+‐MMT (NSM) with various amounts of Na+‐MMT. 相似文献
Surface properties of composites containing chitosan (Ch) with poly(N-vinylpyrrolidone) (PVP) and montmorillonite (MMT) additives were investigated by contact angle measurements, thermogravimetric analysis (TGA), atomic force microscopy (AFM) and tensile tests. Composites were obtained by drop casting suspensions of montmorillonite (1 wt % relative to chitosan) and polymer (1 wt %) in 0.1 mol/dm3 acetic acid. Contact angle measurements for diiodomethane (D) and glycerol (G) on the surfaces of the chitosan films, PVP and their composite films were made; surface free energies were also calculated. It was found that the PVP/MMT or Ch/PVP/MMT blend surface is enriched with a high surface energy component, i.e., polyvinylpyrrolidone. The roughness of chitosan composites increases after the addition of montmorillonite; this may indicate an increase in the heterogeneity of this composition in comparison to other compositions. The TGA thermograms and mass loss percentages at different decomposition temperatures showed that the thermal stability of the binary composite slightly increases upon the addition of polyvinylpyrrolidone. The mechanical properties such as tensile strength and Young modulus depend on the composition and varied non-uniformly. 相似文献