Summary: Styrene‐isoprene‐butadiene rubber/montmorillonite nanocomposites were synthesized by the addition of toluene into clay and living anionic polymerization. These silicate layers (B‐M) were exfoliated within 30 min after polymerization initiation, whereas the layers in the nanocomposites prepared without using toluene (A‐M) were only partially exfoliated and not well‐dispersed in the matrix. The results of TEM and X‐ray diffraction revealed disperse silicates and a strong interaction between the terpolymer matrix and clay in the B‐M nanocomposites. The B‐M‐exfoliated nanocomposites exhibited higher decomposition and glass transition temperatures, storage moduli, tensile strengths and elongations at the break than those of the pure terpolymer and A‐M. With an organophilic montmorillonite (OMMT) content of 3 wt.‐%, the exfoliated nanocomposite exhibited the best thermal stability and mechanical properties. In addition, GPC and 1H NMR results showed that the introduction of OMMT caused a slight increase in the of terpolymer, but hardly affected the microstructure of the terpolymer independent of the preparation method. Thus, the addition of toluene plays an important role in enhancing the dispersion of OMMT, which leads to the improvement of the structure and properties of the B‐M nanocomposites.
In order to establish the structure‐property relationship in the case of clay containing polymer nanocomposites, detailed understanding of silicate layers dispersion into the polymer matrix is necessary. In this study, biodegradable poly[(butylene succinate)‐co‐adipate] (PBSA) was chosen as a model polymer and the nanocomposite of PBSA with organically modified montmorillonite (OMMT) was prepared via the melt‐mixing in a batch mixer. The degree of dispersion of silicate layers in the PBSA matrix was investigated by means of wide angle X‐ray diffraction, small angle X‐ray scattering, high‐annular‐angle‐dark‐field scanning transmission electron microscopy, and high resolution transmission electron microscopy combined with electron tomography. Results demonstrated the homogeneous dispersion of clay platelets in the PBSA matrix. However, the true exfoliation of silicate layers in the polymer matrix is quite difficult to achieve, although there are strong favourable interactions between the polymer matrix and the OMMT surface.
Two novel cationic RAFT agents, PCDBAB and DCTBAB, were anchored onto MMT clay to yield RAFT‐MMT clays. The RAFT‐MMT clays were then dispersed in styrene where thermal self‐initiation polymerization of styrene to give rise to exfoliated PS/clay nanocomposites occurred. The RAFT agents anchored onto the clay layers successfully controlled the polymerization process resulting in controlled molecular masses and narrow polydispersity indices. The nanocomposites prepared showed enhanced thermal stability, which was a function of the clay loading, clay morphology, and slightly on molecular mass.
The oxidative degradation of PP/OMMT nanocomposites under γ‐irradiation was studied. Changes in structure and properties resulting from γ‐exposure in the range 0–100 kGy were investigated. The results were analyzed by comparing the influence of PP‐g‐MA and pristine OMMT on the oxidation kinetics of neat PP. γ‐Irradiation in the presence of air strongly degraded the properties of PP materials, particularly for radiation doses above 20 kGy. The rate of oxidative degradation of PP/OMMT/PP‐g‐MA nanocomposites was much faster than that of neat PP. This suggests that PP‐g‐MA and pristine OMMT components behave as oxidation catalysts, leading to the formation of free radicals in the polymer matrix.
Nanocomposites of poly(ethylene terephthalate) and two different montmorillonite‐based organoclays were prepared by a co‐rotating twin screw extruder. Dispersion of nanoclays in the polymer matrix was examined by TEM and XRD. Nanocomposites with lower content of organoclay showed exfoliated morphology while by increasing the amount of organoclay the intercalated morphology was more prevalent. Both organoclays had a good intercalation with PET and were uniformly dispersed within the polymer. Oxygen permeability of thin films of nanocomposites showed that the nanocomposites had better oxygen barrier properties than the neat PET. Tensile and impact properties of the nanocomposites also were measured.
Fully exfoliated PS/clay nanocomposites were prepared via FRP in dispersion. Na‐MMT clay was pre‐modified using MPTMS before being used in a dispersion polymerization process. The objective of this study was to determine the impact of the clay concentrations on the monomer conversion, the polymer molecular weight, and the morphology and thermal stability of the nanocomposites prepared via dispersion polymerization. DLS and SEM revealed that the particle size decreased and became more uniformly distributed with increasing clay loading. XRD and TEM revealed that nanocomposites at low clay loading yielded exfoliated structures, while intercalated structures were obtained at higher clay loading.
Summary: Three rubber‐based nanocomposites, natural rubber (NR), styrene‐butadiene rubber (SBR), and ethylene‐propylene‐diene rubber (EPDM) matrixes, were prepared with octadecylamine modified fluorohectorite (OC) by melt blending. X‐ray diffraction (XRD) revealed that the SBR/OC and EPDM/OC nanocomposites exhibited a well‐ordered intercalated structure and a disordered intercalated structure, respectively. In the case of the NR/OC nanocomposite, it exhibited an intermediate intercalated and even exfoliated structure. These results were in good agreement with transmission electron microscopy (TEM) observations. Furthermore, in the NR/OC and SBR/OC systems, the mixing process played a predominant role in the formation of nanometer‐scale dispersion structure, whereas the intercalated structure of EPDM/OC formed mainly during the vulcanization process. The tensile strength of SBR/OC and EPDM/OC nanocomposites loading 10 phr OC was 4–5 times higher than the value obtained for the corresponding pure rubber vulcanizate, which could be ascribed to the slippage of the rubber molecules and the orientation of the intercalated OC. For the strain‐induced crystallization NR, the exfoliated OC efficiently improved the modulus of the NR/OC nanocomposite relative to the pure NR. However, its hindrance on NR crystallization during the tensile process may be the main reason for the decrease in tensile strength of NR/OC.
XRD diffraction patterns of three nanocomposites containing 10 phr organoclay. 相似文献
Summary: Ethylene vinyl acetate (EVA) copolymer/dodecyl ammonium ion intercalated montmorillonite (12Me‐MMT) nanocomposites were swelled in xylene under atmospheric condition. Swelling index of these nanocomposites decreased with filler loading indicating that the solvent uptake of these nanocomposites was inversely related to the filler contents. The volume fractions of nanocomposites showed an increasing trend with filler concentration because of unswelling effect exerted by aluminosilicate layers. The cross‐link density was determined using the Flory‐Rehner equation and it was observed that the cross‐link density of these nanocomposites also showed an increasing trend with increasing filler loading. Free energy change (ΔGmix) and the change in entropy (ΔSmix) on swelling of EVA/12Me‐MMT nanocomposites in xylene were calculated and these values reaffirmed that the interaction between polymer chains and silicate layers was very strong which induced remarkable inhibiting ability on EVA matrix when swelled in xylene.
TEM photograph of EVA/12Me‐MMT nanocomposite containing 8 wt.‐% 12Me‐MMT. 相似文献
Summary: A novel rigid PVC ternary nanocomposite containing NBR‐ENP and untreated Na‐MMT has been fabricated. X‐ray diffraction XRD, TEM and SEM observations revealed that the untreated Na‐MMT was exfoliated and most NBR‐ENPs (about 90 nm) were separately dispersed in the PVC matrix. DMTA and TGA demonstrated that the PVC ternary nanocomposites had a higher glass transition temperature and a higher decomposition temperature than neat PVC, while the toughness increased simultaneously. Combustion tests showed that the exfoliated clay in the PVC/NBR‐ENP/MMT ternary nanocomposites did not improve the flame retardancy after ignition under strong heat flux.
Schematic diagram of the fabrication procedure of PVC/NBR‐ENP/Na‐MMT ternary nanocomposites. 相似文献
This paper investigates the effect of both the clay loading and the monomer feed rate on the morphology and properties of poly(styrene‐co‐butyl acrylate)‐clay nanocomposites prepared in emulsion polymerization. Analysis by X‐ray diffraction (XRD) and transmission electron microscopy (TEM) of the nanocomposites prepared by batch polymerization showed that the polymer clay nanocomposites (PCNs) with 1–3 wt.‐% clay loading resulted in intercalated structures, while exfoliated structures were obtained at 10 wt.‐% clay loading. The polymerization was also carried out with semi‐batch polymerization. The morphology, thermal stability, and mechanical properties of nanocomposites obtained were found to be more strongly dependent on the clay/polymer ratio than the monomer feed rate.
Summary: The chemical metallization of aqueous bentonite dispersions afforded stable aqueous hybrid nanoparticle dispersions containing simultaneously dispersed sodium bentonite nanoplatelets together with bentonite supported silver, palladium, or copper nanoparticles with average metal nanoparticle diameters varying between 14 and 40 nm. Such aqueous bentonite/metal hybrid nanoparticle dispersions were blended with cationic PMMA latex to produce PMMA hybrid nanocomposites containing exfoliated polymer‐grafted organoclay together with bentonite supported metal nanoparticles. This dispersion blend formation was investigated with respect to the role of nanostructure formation and mechanical properties. Palladium/bentonite hybrid dispersions were used as catalysts for hydrogenation reactions and the electroless plating of copper. In contrast to the conventional organoclay nanocomposites, the PMMA hybrid nanocomposites, containing simultaneously dispersed organoclay nanoplatelets together with organoclay supported silver nanoparticles, exhibited high antimicrobial activity against the ubiquitous bacterium Staphylococcus aureus, even at low silver content.
Preparation of a polymer hybrid nanocomposite. 相似文献
The effects of heat treatment on the crystal structure and impact strength of poly(phenylene sulfide) (PPS) and nano‐SiOx/ PPS nanocomposites were studied. The molecular weight of heat‐treated neat PPS was increased by 28% due to the crosslinking reaction that changed its crystal morphology. Also, the crystallinity was reduced by 18%, leading to an improvement of the Izod impact strength by 66%. Nano‐SiOx/PPS composites were manufactured by intensive compounding with 3 wt.‐% nano‐SiOx particles treated by an epoxy functional group. Test results showed that the Izod impact strength of nano‐SiOx/heat‐treated PPS composites was 91% better and the crystallinity 27% less compared to the same properties of “as received” neat PPS. Nano‐SiOx has a high specific surface area and a high surface energy; its grafted epoxy group promotes interfacial adhesion with the PPS matrix, hence increasing the Izod impact strength of the nanocomposites.
TEM micrograph of NHTM‐PPS with 3 wt.‐% nano‐SiOx. 相似文献
Summary: To improve the interfacial interaction in MMT‐SBR nanocomposites, one type of UOAC was introduced to in‐situ modified MMT before latex compounding with SBR. The influence of the UOAC/MMT ratio on the structure and properties of MMT/SBR nanocomposites were carefully studied by XRD, TEM, and mechanical testing. It was found that through the in‐situ organic modification, a rubber‐intercalated structure of MMT was obtained in the nanocomposites, and the amount of rubber‐intercalated structure strongly depended on the UOAC/MMT ratio. The tensile strength of MMT‐SBR nanocomposites was enhanced dramatically from 4 to 18 MPa by in‐situ organic modification of MMT.
Stress‐strain diagram of SBR/clay nanocomposites. 相似文献
Summary: Poly(propylene) (PP)/clay nanocomposites have been prepared via a novel reactive compounding approach, in which an epoxy based masterbatch consisting of 20 wt.‐% clay was introduced to poly(propylene) with the aid of a maleic anhydride grafted PP (MAPP). The masterbatch was prepared using a recently developed “slurry compounding” technique. After melt compounding, most clay particles have been exfoliated and dispersed into small stacks with several clay layers. WAXD data shows that the dispersion of clay is better at low clay content or high MAPP content. Due to the novelty of the preparation process and complication of the system, the tensile properties of nanocomposites exhibit some unique tendencies with varying the content of MAPP or masterbatch. It is believed that the yield strength and Young's modulus can be dramatically improved after minimizing the excess of unreacted epoxy and optimizing the dispersion of clay.
TEM micrograph of PP/clay nanocomposites prepared with epoxy based masterbatch. 相似文献
Summary: The fracture toughness of EMC was dramatically increased over a wide temperature range by the addition of a very low volume fraction of layered silicates to EMC filled with micro‐silica particles. Layered silicate‐EMC nanocomposites containing intercalated and the exfoliated silicates were fabricated by using o‐cresol and biphenyl type epoxy resins, respectively. It was found that exfoliated silicates were more effective than intercalated silicates at toughening EMC at temperatures above Tg of the epoxy resin. Enhanced fracture toughness of EMC over a wide temperature range, from ambient to 230 °C has been attributed to the presence of layered silicates, which induces macroscopic crack deflection and severe plastic deformation in front of the crack tip.
xGnP‐Reinforced LLDPE nanocomposites have been prepared using co‐, counter‐ and modified co‐rotating screw systems. The highest tensile strength and modulus were shown in the case of composites made by counter‐rotating screws. The percolation threshold of exfoliated graphite nanoplatelet/LLDPE nanocomposites was between 12 and 15 wt.‐%. The change of crystallinity caused by exfoliated graphite nanoplatelet loading was monitored using DSC and XRD. It was found that solution mixing showed better dispersion of exfoliated graphite nanoplatelets than melt mixing, and counter‐rotating screws produced better dispersion of the exfoliated graphite nanoplatelets than co‐ and modified co‐rotating screws even though bubbling appeared during mixing in the barrel.
A novel zirconia polyester nanocomposite is prepared using an in situ approach. Surface‐functionalized zirconia nanoparticles are obtained by attaching 3‐phosphonopropionic acid to the metal oxide. Neat and surface‐covered metal oxide particles are incorporated at the beginning of the polyesterification reaction of isophthalic acid and neopentyl glycol resulting in zirconia/poly(neopentyl isophthalate) (PNI) nanocomposites. TEM shows that the dispersibility of the inorganic filler is improved by covering the zirconia surface with carboxylic acid groups. These results are verified by SAXS. Rheological measurements reveal that the viscosities are increasing compared to pristine PNI at particle loads of 10 wt% (neat zirconia) and 5 wt% (phosphonic‐acid‐capped zirconia), respectively.
The crystallization behavior of a polyamide 6/organo‐modified montmorillonite (PA 6/OMMT) nanocomposite has been investigated by scanning chip calorimetry and wide‐angle X‐ray scattering, with emphasis placed on the evaluation of the effect of supercooling/cooling rate on the crystal/mesophase polymorphism of the PA 6 matrix. Presence of OMMT has negligible effect on the kinetics of formation of α‐crystals of PA 6 at low cooling rate while there is observed enhanced nucleation of γ‐mesophase on fast cooling. Furthermore, addition of OMMT leads to a distinct increase of the cooling rate required to completely vitrify the amorphous state. The performed experiments demonstrate that the nucleating effect of OMMT in PA 6/OMMT nanocomposites is of particular importance at cooling conditions relevant in polymer processing.
Summary: It is well known that the weight‐average molecular weight ( ) is strictly dependent on conversion in step‐growth polymerizations performed in batch and that the is very sensitive to impurities and molar imbalance. This makes the work of controlling a non trivial job. In this paper a new methodology is introduced for in‐line monitoring and control of conversion and of polyurethanes produced in solution step‐growth polymerizations, based on near‐infrared spectroscopy (NIRS) and torquemetry. A calibration model based on the PLS method is obtained and validated for monomer conversion, while the weight‐average molecular weight is monitored indirectly with the relative shear signal provided by the agitator. Control procedures are then proposed and implemented experimentally to avoid gelation and allow for maximization of . The proposed monitoring and control procedures can also be applied to other step growth polymerizations.
Nanocomposites of linear low‐density polyethylene (LLDPE), with three different amounts of polyhedral oligomeric silsesquioxanes (POSS), were prepared through melt‐mixing in a batch‐mixer at 150 °C. The structure of the prepared nanocomposites was studied by X‐ray scattering and optical microscopy. The surface morphology of the nanocomposites was investigated through field‐emission SEM. The thermal properties of the pure LLDPE and nanocomposites were studied by differential scanning calorimeter (DSC). Thermomechanical properties were assessed on a Paar‐Physics MCR501 rheometer using a solid‐state rectangular fixture. Results exhibited a significant improvement in both the storage and loss moduli of the neat LLDPE upon the incorporation of the POSS particles. A substantial improvement in thermal stability was also observed in the high‐temperature region.
