A comparison of the temperature dependence of the modulus, yield stress and ductility of nanocomposites based on high and low MW PA6 and PA66

Nanocomposites with both organically modified and unmodified silicate have been prepared by an extrusion process using low and high molecular weight grades of PA6 and a low MW grade of PA66. Mechanical properties have been tested at temperatures ranging from 20 to 120 °C. The modulus increase in all nanocomposites with organically modified nanocomposites is similar: at room temperature an increase in the modulus of approximately 10% for each wt% of silicate is found. PA66 nanocomposites display an identical normalized modulus increase as PA6 nanocomposites, while unmodified silicate nanocomposites show a smaller increase in the modulus. The yield stress also increases with the addition of layered silicate. Low MW PA6 and PA66 nanocomposites show brittle fracture behaviour at room temperature, while high MW PA6 nanocomposites are ductile. With increasing temperature all nanocomposites become ductile at a certain temperature.     

Mesua ferrea L. seed oil based acrylate-modified thermostable and biodegradable highly branched polyester resin/clay nanocomposites

Mesua ferrea L. seed oil based highly branched polyester resin was modified by methyl methacrylate through grafting polymerization technique. The nanocomposites of this acrylate-modified polyester and 1–5 wt% loadings of organically modified montmorrilonite (OMMT) nanoclay were prepared by an ex situ technique using strong mechanical mixing and ultrasonication. Formation of nanocomposites was confirmed by X-ray diffractometeric (XRD), scanning electron microscopic (SEM) and transmission electron microscopic (TEM) analyses. The absence of d_{0 0 1} reflections of OMMT in XRD and TEM study revealed the partial exfoliation of OMMT by the polymer chain. The homogeneous surface morphology was also ascertained from SEM. Mechanical and thermal studies of the nanocomposites showed an appreciable improvement in tensile strength and thermal stability by OMMT loading. The enhancement of tensile strength by 2.5 times and thermal stability by 32 °C for 5 wt% OMMT filled nanocomposite was observed compared to that of pristine system. The rheological behavior of the nanocomposites was also investigated and shear thinning was observed. Biodegradation of the nanocomposite films was assayed using two strains of Pseudomonas aeruginosa, SD2 and SD3 and one strain of Bacillus subtilis, MTCC736. The nanocomposites exhibited enhanced biodegradability as compared to pristine acrylate modified polyester. All the results showed the potentiality of the nanocomposites as advanced thin film materials for suitable applications.     

Organically modified-grafted mica (OMGM) nanoparticles for reinforcement of polypropylene

Polypropylene (PP) was reinforced by mica nanoparticles as a reinforcement of mechanical properties. For this purpose, mica was organically modified using diacetone acrylamide, a vinyl functional modifier, to enhance the interaction between the PP chains and mica silicate layers. The X-ray diffraction patterns demonstrated the intercalation of the modifier molecules into the mica gallery. Maleic anhydride-grafted polypropylene was grafted on organically modified mica (OMM) in an organic suspension media at different temperatures, 100, 120, and 130 °C. Fourier transform infrared spectroscopy was used to characterize the OMM and organically modified-grafted mica (OMGM). Various amounts of OMGM nanoparticles, 0–3 wt%, were used to reinforce PP. The effect of OMGM level on the crystallinity, tensile properties, impact, and fracture toughness of resulting nanocomposites was investigated. The results showed that the addition of 1 wt% OMGM, prepared at grafting temperature of 120 °C, enhanced the tensile strength to 12% and notched impact strength to 58%, while it changed the critical stress intensity factor (K _1C) slightly (5%) when compared to PP. Partial exfoliation of OMGM layers in the PP matrix was examined using transmission electron microscopy. The further increase in the OMGM level lowered the mechanical properties and fracture toughness due to OMGM nanoparticle agglomeration.     

The role of preconditioning on morphology development in layered silicate thermoset nanocomposites

The impact of preconditioning constituent materials on the morphology development of organically modified montmorillonite–epoxy nanocomposites is examined to determine the sensitivity of exfoliation to material conditions. In situ synchrotron small‐angle X‐ray scattering studies were performed to relate the initiation and levels of exfoliated morphologies with various silicate preconditioning processes. Significantly, exfoliation could be achieved in systems initially considered intercalated by preconditioning through epoxy–silicate mixture aging. The resulting morphologies lead to slightly improved toughness. Implications for nanocomposite morphology development models include the necessity of further investigation of the complexities of both local and global morphologies. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 89–100, 2004     

Synthesis,structure, and thermal properties of new polypropylene nanocomposites prepared by using MgCl2‐mica/TiCl4 based catalyst

Preparation of polypropylene/mica nanocomposites via in situ polymerization is investigated. The nanocomposites were successfully synthesized using a Ziegler‐Natta catalyst based on MgCl₂/modified mica/TiCl₄. Muscovite mica was organically modified with quaternary ammonium salt, and with triethylaluminum. The treatment with triethylaluminum increased the disorder in the stacking of clay layers, producing a more active catalyst for propylene polymerization, although the mica containing catalysts had lower activity than the standard one prepared without clay. The nanostructure of the composites was characterized by X‐ray diffraction. The results showed that part of the mica layers were exfoliated in the polymer matrix, although tactoids were still present. Small‐angle X‐ray scattering analysis was used to determine how mica and its concentration influence the size of the polymer nanocrystals. Differential scanning calorimetry was used to investigate both melting and crystallization temperatures, as well as the crystallinity of the nanocomposite samples. Thermogravimetric analysis showed that polypropylene/mica nanocomposites presented much higher thermal stability than the polypropylene without mica, which means that mica had a barrier effect against heat. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45587.     

Studies on thermal properties of PS nanocomposites for the effect of intercalated agent with side groups

Polystyrene-layered silicate nanocomposites were prepared from three new organically modified clays by emulsion polymerization method. These nanocomposites were exfoliated up to 3 wt% content of pristine clay relative to the amount of polystyrene (PS). The intercalated agents C₂₀, C₂₀-4VB, and C₂₀-POSS intercalated into the galleries result in improved compatibility between hydrophobic polymer and hydrophilic clay and facilitate the well dispersion of exfoliated clay in the polymer matrix. Results from X-ray diffraction, TEM and Fourier transform infrared spectroscopy indicate that these intercalated agents are indeed intercalated into the clay galleries successfully and these clay platelets are exfoliated in resultant nanocomposites. Thermal analyses of polystyrene-layered silicate nanocomposites compared with virgin PS indicate that the onset degradation temperature ca. 25 °C increased and the maximum reduction in coefficient of thermal expansion (CTE) is ca. 40% for the C₂₀-POSS/clay nanocomposite. In addition, the glass transition temperatures of all these nanocomposites are higher than the virgin PS.     

Characterization of sepiolite as a support of silver catalyst in soot combustion

Turkish sepiolite–zirconium oxide mixtures were applied as a support for the silver catalyst in a soot combustion. Sepiolite–Zr–K–Ag–O catalyst was characterized by XRD, N₂ adsorption, SEM, TPR-H₂ and EGA-MS. The combustion of soot was studied with a thermobalance (TG-DTA). The modification resulted in a partial degradation of the sepiolite structure, however, the morphology was preserved. The adsorption of N₂ of the modified sepiolite is a characteristic for mesoporous materials with a wide distribution of pores. The specific surface area S_BET equals 83 m²/g and the pores volume is 0.23 cm³/g. The basic character of the surface centers of sepiolite is indicated by CO₂ desorption (TPD-MS) at 170 °C and at about 620 °C due to a surface carbonates decomposition. The thermodesorption of oxygen at 650–850 °C indicates the decomposition of AgO_x phases at the surface. The presence of AgO_x phases is also confirmed by TPR-H₂ spectrum (low temperature reduction peak at 130 and 180 °C). The high-temperature reduction at about 570 °C is probably related to Ag–O–M phases on the support.The soot combustion takes place at T₅₀ = 575 °C. Without silver (sepiolite–Zr–K–O) T₅₀ = 560 °C but sepiolite modified with silver (sepiolite–Zr–K–Ag–O) undergoes the same process at T₅₀ = 490 °C.     

Rheological,mechanical, optical,and transport properties of blown films of polyamide 6/residual monomer/montmorillonite nanocomposites

Exfoliated nanocomposites of polyamide 6 (PA6) with residual monomer and an organically treated montmorillonite (3 and 5 wt %) were produced by twin‐screw extrusion. The composites had their steady state, dynamic, and transient rheological properties measured by parallel‐plates rheometry; their exfoliation level was characterized by wide angle X‐rays diffraction (WAXD) and transmission electron microscopy (TEM). The characterization showed as follows: (i) the nanoclay's lamellas were well dispersed and distributed thru the PA6, (ii) the postpolymerization of the residual monomer produced more branched chains than linear ones in the pure PA6, (iii) the nanoclay's lamellas acted as entanglement points in the nanocomposites, and (iv) the molecular weight of the PA6 in the nanocomposites decreased. Blown films of the nanocomposites were produced by single screw extrusion; the die pressure during the film blowing of the nanocomposites strongly decreased. The tensile mechanical properties of the blown films were also measured. Along the machine direction (MD), the best mechanical properties were obtained with the 5 wt % nanocomposite, whereas along the transverse direction (TD), the 3 wt % nanocomposite had the best behavior. The glass transition temperature (T_g) of the blown films was measured by dynamic mechanical thermal analyses (DMTA). The 5 wt % nanocomposite had the highest T_g of all the films. The optical properties were measured by spectrophotometry; the nanoclay decreased the films' haze, but the level of transmittance was not affected. The water vapor and oxygen permeability rates of the nanocomposites films were found to be lower than in the pure PA6 blown film as a result of a tortuosity effect. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Adsorption and binding of the transgenic plant proteins, human serum albumin, β-glucuronidase, and Cry3Bb1, on montmorillonite and kaolinite: Microbial utilization and enzymatic activity of free and clay-bound proteins

Human serum albumin (HSA), β-glucuronidase (GUS), and the Cry3Bb1 protein from Bacillus thuringiensis subsp. kumamotoensis are expressed by genetically-modified plants. Commercial samples of these proteins adsorbed and bound rapidly on the clay minerals, kaolinite (K) and montmorillonite (M). Adsorption increased as the concentration of protein increased and then reached a plateau. The greatest amount of adsorption and binding occurred with the Cry3Bb1 protein, of which there was no desorption: 6.7 ±0.21 μg adsorbed and bound μg^− 1 of M; 2.1 ± 0.39 μg adsorbed and bound μg^− 1 of K. With GUS, 2.2 ± 0.29 μg adsorbed and 1.7 ±0.21 μg bound μg^− 1 of M; 1.5 ± 0.28 μg adsorbed and 1.0 ± 0.03 μg bound μg^− 1 of K. HSA was adsorbed and bound the least: 1.2 ±0.04 μg adsorbed and 0.8 ± 0.05 μg bound μg^− 1 of M; 0.4 ± 0.05 μg adsorbed and 0.4 ± 0.03 μg bound μg^− 1 of K. However, X-ray diffraction analyses indicated that only HSA intercalated M, and none of the proteins intercalated K, a nonswelling clay. When bound, the proteins were not utilized for growth by mixed cultures of soil microorganisms, whereas the cultures readily utilized the free (i.e., not adsorbed or bound) proteins as sources of carbon and energy. The enzymatic activity of GUS was significantly enhanced when bound on the clay minerals. These results indicated that recombinant proteins expressed by transgenic plants could persist and function in soil after release in root exudates and from decaying plant residues as the result of the protection provided against biodegradation by binding on clay minerals.     

Preparation and swelling properties of superabsorbent nanocomposites based on natural guar gum and organo-vermiculite

Vermiculite (VMT) was modified with cetyl trimethylammonium bromide (CTAB). Superabsorbent nanocomposites were prepared by solution polymerization of natural guar gum (GG), partially neutralized acrylic acid (NaA) and organo-vermiculite (CTA⁺-VMT), ammonium persulfate (APS) as initiator and N,N′-methylene-bis-acrylamide (MBA) as crosslinking agent. FTIR spectra confirmed that NaA had been grafted onto GG and the OH groups of CTA⁺-VMT participated in the polymerization reaction. The intercalated-VMT was exfoliated during polymerization and uniformly dispersed in the GG-g-PNaA matrix. Swelling tests show that CTA⁺-VMT improved swelling and swelling rate more remarkably than VMT, and the nanocomposite exhibited distinct kinetic swelling behavior in NaCl and CaCl₂ solution. Organo-VMT improved the gel strength of the nanocomposite compared to VMT, and the maximum storage modulus of the nanocomposite reached 658 Pa (γ = 0.5%, ω = 100 rad/s).     

Dielectric spectroscopy during extrusion processing of polymer nanocomposites: a high throughput processing/characterization method to measure layered silicate content and exfoliation

Dielectric spectroscopy was conducted during extrusion processing of polyamide-6 (PA6) and layered silicate/polyamide-6 nanocomposites. Dielectric dispersion parameters were identified that appear sensitive to layered silicate concentration and degree of exfoliation. Specific to measuring layered silicate concentration is that the Maxwell-Wagner strength of dispersion, Δε_mw, increases linearly with the % mass fraction layered silicate content. This relationship is independent of exfoliation resulting in nanomorphology-averaged Δε_mw values that reflect layered silicate concentration; i.e. 12,800±519 indicates 1.29% mass fraction of a layered silicate in PA6. The nanomorphology is primarily reflected in the Maxwell-Wagner characteristic relaxation frequency value, f_mw, where, for example, 80.4±5 Hz indicates a mixed intercalated/exfoliated nanomorphology. However, following the nanomorphology with the f_mw value can in some cases be complicated because different nanomorphologies can yield the same f_mw value. In these cases we have found that there is a significant difference in the conductive resistance and segmental mobility of these polymers, as indicated by the σ_DC and fα values. For example, the intercalated and exfoliated nanocomposites have a f_mw value of about 5.1 Hz, but the exfoliated nanocomposites have σ_DC and fα values that are much larger than determined for the intercalated nanocomposites.     

Synthesis and antimicrobial activity of the Schiff base from polyoxyalkylene‐montmorillonite nanocomposites and aldehydes

Vanillin (4‐hydroxy‐3‐methoxy benzaldehyde) and 5‐formylamino salicylic acid microbicides were reacted with polyoxyalkylene‐montmorillonite (D_230–2000‐MMT) nanocomposites. The microstructure of these Schiff base nanocomposites was characterized by TEM and XRD. D_230–2000‐MMT nanocomposites were prepared by an ion exchange process of sodium montmorillonite (Na‐MMT) and NH₃ ⁺ groups in polyoxyalkylene amine hydrochloride with three different molecular masses of D₂₃₀, D₄₀₀, and D₂₀₀₀. Wide‐angle X‐ray diffraction confirms the intercalation of the polymer between the silicate layers. Electrostatic interaction between the positively charged NH₃ ⁺ groups and the negatively charged surface of MMT was observed. The nanocomposites were tested for antimicrobial activity against the Gram‐negative bacteria (Escherichia coli NCIM 2065), Gram‐positive bacteria (Bacillus subtillus ATCC), and fungi (Candida albicans SC5314 and Cryptococcus neoformans). The D₂₀₀₀‐MMT/vanillin Schiff base nanocomposite strongly inhibited the growth of all microorganisms that can be used in different applications. The amount of loaded polymer and the structure of the nanocomposite play an important role in inhibiting the bacterial and fungal strains. It is found that the Schiff base nanocomposite affect the morphology, oxygen consumption, and the release of cytoplasmic constituents such as potassium (K⁺), sodium (Na⁺), and calcium (Ca²⁺) ions leading to death of the cells. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Oxygen diffusion into polystyrene–bentonite films

A simple fluorescence technique is proposed for the measurement of the diffusion coefficient of oxygen into polystyrene–clay composite films. The composite films were prepared from the mixture of surfactant-free pyrene (P)-labeled polystyrene latexes (PS) and modified bentonite (MNaLB) at various compositions at room temperature. These films were annealed at 200 °C above the glass transition (T_g) temperature of polystyrene for 10 min. Oxygen diffusion into the films was monitored with steady state fluorescence (SSF) measurements. Measurements were performed at room temperature for different film compositions (0, 5, 10, 20, 30, 50 and 60 mass% modified bentonite) films to evaluate the effect of MNaLB content on oxygen diffusion. The diffusion coefficient, D of oxygen was determined by the fluorescence quenching method by assuming Fickian transport and increased from 7.4 × 10^− 10 to 26.9 × 10^− 10 cm² s^− 1 with increasing MNaLB content. This increase in D value was explained by formation of microvoids in the film. These voids are large enough to contribute to the penetration of oxygen molecules through the films. The montmorillonite content did not affect the quenching rate constant, k_q and mutual diffusion coefficient, D_m values.     

Homopolymerization effects in polymer layered silicate nanocomposites based upon epoxy resin: Implications for exfoliation

Exfoliation of polymer layered silicate nanocomposites based upon epoxy resin has previously been reported to be enhanced by allowing some homopolymerization of the resin to occur, catalyzed by the onium ion of the organically modified clay, before the addition of the cross‐linking agent and the curing of the nanocomposite. In this work we examine the effects of homopolymerization induced by pre‐conditioning the resin/clay mixtures by storing them at various temperatures, from room temperature to 100°C, prior to curing. It is found that pre‐conditioning results in similar increases in both the epoxy equivalent (EE) and the glass transition temperature (T_g) of the resin as a consequence of homopolymerization, with a linear relationship between EE and T_g that depends on the pre‐conditioning temperature. This is attributed to two different homopolymerization reaction mechanisms, activated monomer (AM) and activated chain end (ACE), the former dominating at high temperature and the latter at low temperature. The effects of these homopolymerization reactions on the network and nanostructure of the nanocomposite are discussed, the important aspect emerging being that the ACE mechanism is the one that most significantly enhances the exfoliation process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of organic modifiers and silicate type on filler dispersion,thermal, and mechanical properties of ABS‐clay nanocomposites

Acrylonitrile–butadiene–styrene (ABS)–clay composite and intercalated nanocomposites were prepared by melt processing, using Na‐montmorillonite (MMT), several chemically different organically modified MMT (OMMT) and Na‐laponite clays. The polymer–clay hybrids were characterized by WAXD, TEM, DSC, TGA, tensile, and impact tests. Intercalated nanocomposites are formed with organoclays, a composite is obtained with unmodified MMT, and the nanocomposite based on synthetic laponite is almost exfoliated. An unintercalated nanocomposite is formed by one of the organically modified clays, with similar overall stack dispersion as compared to the intercalated nanocomposites. T_g of ABS is unaffected by incorporation of the silicate filler in its matrix upto 4 wt % loading for different aspect ratios and organic modifications. A significant improvement in the onset of thermal decomposition (40–44°C at 4 wt % organoclay) is seen. The Young's modulus shows improvement, the elongation‐at‐break shows reduction, and the tensile strength shows improvement. Notched and unnotched impact strength of the intercalated MMT nanocomposites is lower as compared to that of ABS matrix. However, laponite and overexchanged organomontmorillonite clay lead to improvement in ductility. For the MMT clays, the Young's modulus (E) correlates with the intercalation change in organoclay interlayer separation (Δd₀₀₁) as influenced by the chemistry of the modifier. Although ABS‐laponite composites are exfoliated, the intercalated OMMT‐based nanocomposites show greater improvement in modulus. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mesua ferrea L. seed oil based acrylate-modified thermostable and biodegradable highly branched polyester resin/clay nanocomposites

Mesua ferrea L. seed oil based highly branched polyester resin was modified by methyl methacrylate through grafting polymerization technique. The nanocomposites of this acrylate-modified polyester and 1–5 wt% loadings of organically modified montmorrilonite (OMMT) nanoclay were prepared by an ex situ technique using strong mechanical mixing and ultrasonication. Formation of nanocomposites was confirmed by X-ray diffractometeric (XRD), scanning electron microscopic (SEM) and transmission electron microscopic (TEM) analyses. The absence of d_0 0 1 reflections of OMMT in XRD and TEM study revealed the partial exfoliation of OMMT by the polymer chain. The homogeneous surface morphology was also ascertained from SEM. Mechanical and thermal studies of the nanocomposites showed an appreciable improvement in tensile strength and thermal stability by OMMT loading. The enhancement of tensile strength by 2.5 times and thermal stability by 32 °C for 5 wt% OMMT filled nanocomposite was observed compared to that of pristine system. The rheological behavior of the nanocomposites was also investigated and shear thinning was observed. Biodegradation of the nanocomposite films was assayed using two strains of Pseudomonas aeruginosa, SD2 and SD3 and one strain of Bacillus subtilis, MTCC736. The nanocomposites exhibited enhanced biodegradability as compared to pristine acrylate modified polyester. All the results showed the potentiality of the nanocomposites as advanced thin film materials for suitable applications.     

Enhanced electrical and electrochemical properties of PMMA-clay nanocomposite gel polymer electrolytes

In the present work, effect of organically modified montmorillonite (MMT) clays on PMMA-based electrolytes has been investigated. The nanocomposites have been prepared by solution intercalation technique with varying clay loading from 0 to 5 wt.%. The formation of partially exfoliated nanocomposites has been confirmed by XRD and TEM analyses. The obtained nanocomposites were soaked with 1 M LiClO₄ in 1:1 (v/v) solution of propylene carbonate (PC) and diethyl carbonate (DEC) to get the required gel electrolytes. Surface morphology and structural conformation of the nanocomposite electrolytes have been examined by SEM and FTIR analyses, respectively. It has been observed that the ionic conductivity of the nanocomposite gel polymer electrolytes increases with the increase in clay loading and attains a maximum value of 1.3 × 10⁻³ S/cm at room temperature as revealed by ac impedance spectroscopy. Improvement of electrochemical and interfacial stabilities has also been observed in the gel electrolytes containing MMT fillers.     

Polymer-layered silicate nanocomposites prepared through in situ reversible addition-fragmentation chain transfer (RAFT) polymerization

Reversible addition-fragmentation chain transfer (RAFT) polymerizations were performed in the presence of organically modified clays and successfully prepared polystyrene-, poly(methyl methacrylate)-, and poly(n-butyl acrylate)-layered silicate nanocomposites. The polymers had well-defined molecular weights and low polydispersities, as expected from RAFT polymerizations. The morphology of polystyrene-, and poly(n-butyl acrylate)-nanocomposites were found to be exfoliated using montmorillonite modified with N,N-dimethyl-n-hexadecyl-(4-vinylbenzyl) ammonium (MMT-VB16). In the case of PMMA nanocomposite, the structure was a mixture of intercalated and exfoliated when MMT-VB16 was used, while the use of montmorillonite modified with 2-methacryloyloxyethyl-hexadecyldimethyl ammonium (MMT-MA16) resulted in exfoliation.     

Rheological characterization of polystyrene-clay nanocomposites to compare the degree of exfoliation and dispersion

Polymer-clay nanocomposites are of great interest due to their improvement in certain material properties relative to virgin polymer or conventional composites. For example, compared to conventional materials, Nylon 6/montmorillonite nanocomposites demonstrated significant improvements, including high strength, high modulus and high heat distortion temperature. Because viscoelastic measurements are highly sensitive to the nanoscale and mesoscale structure of polymeric materials, when combined with X-ray scattering, electron microscopy, thermal analysis, and mechanical property measurements, they will provide fundamental understanding of the state and mechanism of exfoliation of the layered silicate (clay) in a polymer matrix. In addition, understanding rheological properties of polymer nanocomposites is crucial for application development and understanding polymer processability.The objective of this research is to develop a rheological technique to analyze the clay morphology in nanocomposite. Previous work has demonstrated the utility of the rheological technique to differentiate (qualify) the degree of exfoliation/dispersion. This report utilizes findings from the earlier work to further map out the structure-rheological response of polystyrene nanocomposites with various composition, clay types, and dispersion; and to quantify the key parameter that dominates the characteristic rheological response. This report explored a series of polystyrene (PS)-clay nanocomposites with 1,2-dimethyl-3-n-hexadecyl imidazolium (DMHDI) organically modified clays. These PS nanocomposites investigated here demonstrated a change of pattern in dynamic mechanical spectrum, as a function of the degree of exfoliation, from typical polymer response to a terminal response of [G′∼ω, G″∼ω], then to a pattern with double crossover frequencies, and finally to a solid-like response with G′>G″ in all frequency ranges. We showed that the number of particles per unit volume is a key factor determining the characteristic response of nanocomposites.In addition, the rheological response of PS-clays nanocomposite made from DMHDI modified clay combined with high-energy sonication (characterized as exfoliated by XRD and TEM) was compared with that of nanocomposites made by dimethyl, benzyl hydrogenated tallow (2MBHT) modified clay. We found that PS nanocomposites made by DMHDI-modified clay with high-energy sonication are better dispersed than the nanocomposites made previously using 2MBHT-modified clay. We also showed that the glass transition temperatures were not very sensitive to the degree of dispersion.The key finding of this research is that rheological measurements are complimentary to traditional polymer nanocomposite analysis techniques, and they may also serve as an analytical tool by itself (under appropriate conditions), now that some fundamental behavior has been identified.     

Comparative photo‐oxidation under natural and accelerated conditions of polypropylene nanocomposites produced by extrusion and injection molding

The photo‐oxidation behavior under natural and accelerated conditions of polypropylene/layered silicate nanocomposite is studied in this article. The nanocomposites are prepared via simple melt mixing (extrusion and injection molding). The structure obtained is very dependent on the preparation mode and the modified clay used; mostly, exfoliation structure is produced. The nanocomposites start their photo‐degradation earlier than the control samples polypropylene and polypropylene‐graft‐maleic anhydride with a higher oxidation rate for specimen produced by injection molding. This is explained by the presence of organiphilic‐modified montmorillonite layers that trap the oxygen, increasing the oxygen pressure in the bulk and leading to a decrease of the induction period. Contrary to the control samples that display auto acceleration in their oxidation kinetics, the nanocomposites show a slight tendency to a plateau indicating a slowing down of the photo‐oxidation process. This is ascribed to oxygen starvation that occurs in the nanocomposite. The acceleration factor is found to be higher for the nanocomposite comparatively of the control samples. With the aid of SF₄ and NO treatments, the mechanism of photo degradation was found to be similar in PPgMA and its nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007