Vermiculite (VMT) was successfully modified by cationic exchange of hexadecyltrimethyl ammonium ions, covalent grafting of glycidoxypropyl trimethoxy silane, and combining grafting and intercalation. The complete removal of excess surfactant from VMT resulted in a change in the interlayer structure and higher thermal stability of the organoclay mineral. The organosilane grafted on the clay mineral edges improved the thermal stability of the organoclay mineral. The organoclay minerals were melt compounded with poly(l-lactic acid) (PLLA), and the effect of the nanofiller concentration, type of modification and organoclay mineral purity on the nanostructure and thermal properties of nanocomposites was investigated. The removal of excess surfactant and organosilane functionalization enhanced the dispersion level of the organoclay mineral. PLLA degradation that occurred during nanocomposite processing depended on the clay mineral concentration, the extent of clean surface and the clay mineral dispersion state. The removal of excess surfactant and organosilane functionalization improved the thermal stability of nanocomposites. 相似文献
Montmorillonite K-10 clay was surface-modified using the cationic surfactants viz., butyltriphenylphosphonium bromide (BTPB), cetyltrimethylammonium bromide (CTAB), and tributylhexadecylphosphonium (TBHPB) bromide. Of these, CTAB and TBHPB modified clays were chosen for surface grafting with 3-aminopropyltrimethoxy silane (APTMS) coupling agent. The nanocomposites were fully characterized by powder X-ray diffraction (XRD), solid state 29Si NMR, Fourier transform infrared spectroscopy (FTIR) and thermogravimetry (TGA). The XRD and FTIR confirmed the increase in basal plane spacing and intercalation of long chain surfactant molecules into the clay gallery, while TGA indicated the onset degradation and 10% weight loss temperature (T10%) in case of quaternary phosphonium modified clay that was higher than the corresponding ammonium counterpart; these values increased further after the grafting with APTMS. The 29Si NMR peak deconvolution study suggested that the molar % of T units and total degree of silica condensation for different APTMS grafted clay samples were more than 20% and 80%, respectively. 相似文献
Summary Recycled PVC/clay nanocomposites were prepared by melt mixing of recycled PVCs and modified clays. Characterization of the nanostructure of the nanocomposites was carried out using wide angle X-ray diffraction (WAXD) and transmission electron microscopy(TEM). In case of 10wt.%, the characteristic peak of modified clay was perfectly disappeared, because of aids of plasticizers as co-intercalator. Thermal stability was evaluated from the thermal decomposition behaviors and linear dimension changes by TGA and TMA system. Coefficients of thermal expansion of the nanocomposites were also observed from TMA analysis. Dynamic mechanical properties were evaluated using DMA system. The thermal and mechanical properties of the nanocomposites were improved simultaneously for varied clay loadings, 1,3,5,10wt.%, compared to recycled PVC. Especially, the storage modulus of the nanocomposites with 10wt.% clay loading was increased 11 times compared to that of recycled PVC. 相似文献
Summary: Linear low‐density polyethylene (LLDPE)/clay nanocomposites are obtained and studied by using a zinc‐neutralized carboxylate ionomer as a compatibilizer. LLDPE‐g‐MA is used as a reference compatibilizer. Two different clays, natural montmorillonite (Closite Na+) and a chemically modified clay Closite 20A have been used. Nanocomposites are prepared by melt blending in a twin‐screw extruder using two mixing methods: two‐step mixing and one‐step mixing. The relative influence of each compatibilizer is determined by wide‐angle X‐ray diffraction structural analysis and mechanical properties. The results are analyzed in terms of the effect of the compatibilizing agent and incorporation method in the clay dispersion, and the mechanical properties of the nanocomposites. Experimental results confirm that the film samples with ionomer show a good mechanical performance only slightly below that of the samples with maleic anhydride (MA). The two‐step mixing conditions result in better dispersion and intercalation for the nanofillers than one‐step mixing. The exfoliation of clay platelets leads to an improved thermal stability of the composite. The oxygen permeability of the clay nanocomposites, using ionomer as a compatibilizer, is decreased by the addition of the clay.
TEM image of a PE/4 wt.‐% Closite 20A nanocomposite formed using ionomer. 相似文献
In this study, a modified montmorillonite (W-H-OMMT) was prepared by intercalating pristine montmorillonite using a phosphorus salt and a subsequent grafting using a long-alkyl-chain silane, and the nanocomposites with poly[styrene–(ethylene-co-butylene)–styrene] (SEBS) were prepared by melt blending. The pristine and the modified MMT were characterized by XRD, FT-IR, XPS and SEM. The morphology of the SEBS nanocomposites was studied using XRD, SEM and TEM, and the results can be correlated well with transparency, color, surface contact angle, rheological behavior, thermal and mechanical properties of the nanocomposites. As compared with pristine and the modified clay, more uniform dispersion and improved compatibility are observed for the W-H-OMMT in the SEBS matrix, resulting in better transparency and more hydrophobic surface for the SEBS/W-H-OMMT nanocomposite. Better thermal stability, a synergetic effect in tensile strength and elongation at break were observed, which can be attributed to well dispersion of the W-H-OMMT, as well as perfect adhesion between the W-H-OMMT and the SEBS matrix from the enhanced molecular interaction between the long-alkyl chain and the SEBS molecules. Compared to pure SEBS, the strength and elongation of SEBS/W-H-OMMT nanocomposite increased by 8.5 and 7.6 %; meanwhile, the water contact angel and the 50 % weight loss temperature increased by 5.3 and 13.1 %, respectively. Appropriate silane grafted organic montmorillonite provided an efficient way for the overall performance improvement of SEBS. 相似文献
Since the end of the last century, the discovery of polymer nanocomposites and their ever-expanding use in various applications has been the result of continuous developments in polymer science and nanotechnology. In that regard, progress in developments on the use of modified natural and synthetic clays for designing polymer nanocomposites is presented herein. The modified clays used in composite preparation include natural clays such as montmorrilonite, hectorite, sepiolite, laponite, saponite, rectorite, bentonite, vermiculite, biedellite, kaolinite, and chlorite, as well as synthetic clays including various layered double hydroxides, synthetic montmorrilonite, hectorite, etc. The preparation, structure and properties of polymer nanocomposites using the modified clays are discussed. Even at a low loading, these composites are endowed with remarkably enhanced mechanical, thermal, dynamic mechanical, adhesion and barrier properties, flame retardancy, etc. The properties of the nanocomposites depend significantly on the chemistry of polymer matrices, nature of clays, their modification and the preparation methods. The uniform dispersion of clays in polymer matrices is a general prerequisite for achieving improved mechanical and physical characteristics. Various theories and models used to design polymer/clay nanocomposites have also been highlighted. A synopsis of the applications of these advanced, high-performance polymer nanocomposites is presented, pointing out gaps to motivate potential research in this field. 相似文献
In the present paper, three ammonium salts namely, tetraethylammonium bromide (TEAB), tetrabutylammonium bromide (TBAB), and
cetyltrimethylammonium bromide (CTAB) were employed to prepare organoclay by cation exchange process. Polystyrene (PS) /clay
nanocomposites were prepared by melt blending using commercial nanoclay and organoclays prepared using above mentioned salts.
X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis indicated that the modified clays were intercalated
and/or exfoliated into the polystyrene matrix to a higher extent than the commercial nanoclay. Further, amongst the modified
organoclays, TBAB modified clay showed maximum intercalation of clay layers and also exfoliation to some extent into the polystyrene
matrix. TEM micrograph exhibited that TBAB modified clay had the best nanoscale dispersion with clay platelet thickness of
∼6–7 nm only. The mechanical properties of the nanocomposites such as tensile, flexural and izod impact strength were measured
and analyzed in relation to their morphology. We observed a significant improvement in the mechanical properties of polystyrene/clay
nanocomposites prepared with modified clays as compared to commercial organoclay, which followed the order as; PS/TBAB system
> PS/CTAB system > PS/TEAB system. Thermogravimetric analysis (TGA) demonstrated that T10, T50 and Tmax were more in case of polystyrene nanocomposites prepared using modified organoclays than nanoclay [nanolin DK4]
and maximum being in the case of PS/CTAB system. The results of Differential Scanning Calorimetry (DSC) confirmed that the
glass transition temperature of all the nanocomposites was higher as compared to neat polystyrene. The nanocomposites having
2% of TBAB modified clay showed better oxygen barrier performance as compared to polystyrene. 相似文献
The compatibilization effects provided by an amine silane modified polyethylene (PEgAS) versus those by a maleated polyethylene
(PEgMA), for forming PE–clay based nanocomposites, were studied. PEgAS was prepared by condensation reaction between PEgMA
and g-(aminopropyl) triethoxy silane (APTS). It had the triethoxy-silane functionality on one end and was solution mixed with
an organomodified clay (Cloisite 20A) to promote the reaction of the silane groups with the hydroxyl groups on the surface
of the clay. The obtained masterbatches were then compounded with PE to obtain PE–clay nanocomposites by melt blending in
a twin screw extruder, using different compatibilizers and clay contents. FTIR, XRD, STEM, and Instron were used to characterize
the structural, morphological, and mechanical properties of the nanocomposites. Results showed that the PEgAS formed more
exfoliated–intercalated morphology and better mechanical properties, especially in modulus and tensile strength as compared
with PEgMA composites and neat PE. The Young modulus was 35% higher, and the tensile strength was 18% higher with PEgAS composites. 相似文献
Poly (styrene-acrylonitrile) (SAN)/clay nanocomposites have successfully been prepared by melt intercalation method. The hexadecyl triphenyl phosphonium bromide (P16) and cetyl pyridium chloride (CPC) are used to modify the montmorillonite (MMT). The structure and thermal stability property of the organic modified MMT are, respectively characterized by Fourier transfer infrared (FT-IR) spectra, X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The results indicate that the cationic surfactants intercalate into the gallery of MMT and the organic-modified MMT by P16 and CPC has higher thermal stability than hexadecyl trimethyl ammonium bromide (C16) modified MMT. The influences of the different organic modified MMT on the structure and properties of the SAN/clay nanocomposites are investigated by XRD, transmission electronic microscopy (TEM), high-resolution electron microscopy (HREM), TGA and dynamic mechanical analysis (DMA), respectively. The results indicate that the SAN cannot intercalate into the interlayers of the pristine MMT and results in microcomposites. However, the dispersion of the organic-modified MMT in the SAN is rather facile and the SAN nanocomposites reveal an intermediate morphology, an intercalated structure with some exfoliation and the presence of small tactoids. The thermal stability and the char residue at 700°C of the SAN/clay nanocomposites have remarkably enhancements compared with pure SAN. DMA measurements show that the silicate clays improve the storage modulus and glass transition temperature (Tg) of the SAN matrix in the nanocomposites. 相似文献