Chemorheology and properties of epoxy/layered silicate nanocomposites

The effect of the organoclay nanoparticles on the rheology and development of the morphology and properties for epoxy/organoclay nanocomposites has been studied. The interlayer spacing increases with the temperature of cure resulting in intercalated morphologies with varying degrees of interlayer expansion, depending on the cure temperature used. Rheological studies of the curing process indicate that intergallery diffusion before curing is essential for exfoliation, before the morphology is frozen in by gelation and vitrification. The maximum increase in modulus was observed for the 2 wt% clay loading. Viscoelastic behavior and mechanical properties of the cured samples were correlated with the morphological and rheological study.     

Preparation and characterization of polypropylene/layered silicate nanocomposites using an antioxidant

Polypropylene (PP)/layered silicate nanocomposites were prepared via simple melt mixing of three components, PP, layered silicates modified with octadecylamine (C18-MMT) and antioxidant, to investigate the role of antioxidant. TEM and X-ray scattering results confirmed the intercalated state of silicates in PP/layered silicate nanocomposites with antioxidant. In rheological and mechanical study, the nanocomposites with antioxidant showed higher properties than those of the unfilled PP. The nanocomposite with 5 wt% C18-MMT and 0.5 phr antioxidant exhibited about 1.4 times higher tensile modulus and 1.3 times higher storage modulus than the unfilled PP. However, PP/C18-MMT without antioxidant showed lower rheological values owing to the thermal decomposition of PP and the poor compatibility between PP and C18-MMT. It could be concluded that antioxidants played an important role in enhancing the compatibility between PP and C18-MMT. According to the real time X-ray diffraction, the nanocomposite showed the weak ordering of PP crystals than the unfilled PP in the load-extension plateau region of elongation.     

Preparation and characterization of nanocomposites based on chitosan with ZnO-Curcumin

The present paper studied the possibility to obtain nanocomposites of chitosan incorporated with ZnO NP, whose surface has been modified with bioactive compounds. To obtain ZnO nanoparticles, the biogenic method was used and the anchoring of curcumin (CRC) on the surface of the particles was followed. Chitosan-based ZnO-CRC were synthesized using ex-situ method that involves the separate preparation of ZnO particles and their dispersion in the chitosan matrix by mechanical and ultrasonic mixing. The structural and morphological studies of the synthesized samples were carried out using X-ray diffraction, SEM microscopy, FTIR and EDX spectroscopy, and the wetting capacity. The XRD analysis revealed wurtzite crystalline structure of ZnO, anchoring of curcumin to the oxide surface, with an average crystallite size about 18.7 nm. The morphological study shows that the particles have spherical formations, with dimensions in the nanometric range and a relatively uniform distribution of ZnO particles in the matrix. Elemental composition of samples was identified using EDX analysis. Contact angle was measured to evaluate the hydrophilic and/or hydrophobic character of the surfaces. The results demonstrate that the synthesized materials have morpho-structural and wetting characteristics that allow the extension of applicability in biotechnological fields as coating systems.     

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.     

Electrospinning of poly(MMA-co-MAA) copolymers and their layered silicate nanocomposites for improved thermal properties

Copolymers consisting of methyl methacrylate (MMA) and methacrylic acid (MAA) and their layered silicate nanocomposites were electrospun to form fibers with diameters in the sub-micron range. The presence of MAA increased the T_g and thermal stability of the copolymers through formation of anhydrides upon heating. Fibers of uniform diameters were obtained for the poly(MMA-co-MAA) copolymers and nanocomposites containing montmorillonite (MMT), while protrusions were observed on the electrospun fibers from nanocomposites containing fluorohectorite (FH). The electrospinnability of copolymer solutions and nanocomposite dispersions predicted based on both rheological analyses and conductivity measurements correlates well with the experimental electrospinning observations. Dispersion of clays within the nanocomposites improved the electrospinnability of the nanocomposite dispersions. MMT is predominantly exfoliated and well distributed within the fiber and oriented along the fiber axis. Char formation was observed when the MMT-containing fibers were heated above the decomposition temperature, indicating a potential for reduced flammability and increased self-extinguishing properties, whereas the FH-containing materials disintegrated into either film or powder form.     

Multiwalled carbon nanotube/polybenzoxazine nanocomposites: Preparation, characterization and properties

A novel nanocomposite composed of polybenzoxazine (PBZ) and multiwalled carbon nanotubes (MWNT) was prepared successfully. The surface modification of MWNT, including nitric acid modification followed by toluene-2,4-diisocyanate (TDI) treatment, introduced hydroxyl, carboxyl, and isocyanate groups on the MWNT surface. The surface carboxyl groups catalyzed the ring-opening reaction of benzoxazine and thus decreased the curing temperature of the system. The isocyanate groups reacted with the phenolic hydroxyl groups generated by the ring opening of benzoxazine resulting in the significant improvement of the adhesion between PBZ and MWNT. Dynamic mechanical analyses indicated the increase of storage modulus as well as T_g by the addition of MWNT into PBZ. A well dispersed modified-MWNT on nanoscale level inside PBZ matrix was observed by TEM and SEM.     

Antibacterial activity of chitosan grafting nisin: Preparation and characterization

Nisin grafted chitosan was prepared by using microbial transglutaminase as biocatalyst. The transglutaminase-catalyzed reaction displayed high efficiency, high selectivity, mild reaction condition and environmental friendliness. The results revealed that the degree of substitution (DS) of nisin–chitosan could be controlled by adjusting the reaction time, the reaction temperature and the molar ratio of nisin to chitosan. And nisin–chitosan in different pH showed excellent solubility. In addition, in vitro antibacterial activity assessment, nisin–chitosan with the concentration of 0.008 mg/mL showed pronounced inhibitory effect against Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis) and Gram-negative bacteria (Escherichia coli). Furthermore, L929 mouse fibroblasts were cultured with nisin–chitosan, and the methylthiazol tetrazolium (MTT) assay showed that nisin–chitosan with the concentration from 0.005 to 0.01 mg/mL displayed low toxicity. The results may contribute to finding the application of nisin–chitosan in pharmaceutical and food industry fields.     

Poly(ethylene 2,6-naphthalate)/layered silicate nanocomposites: fabrication, crystallization behavior and properties

In this study, poly(ethylene 2,6-naphthalate) (PEN)/layered silicate nanocomposites (PLSNs) were successfully prepared by the intercalation of PEN polymer into organically-modified layered montmorillonite through the melt blending process. Both X-ray diffraction data and transmission electron microscopy images of PEN/layered silicate nanocomposites indicate most of the swellable silicate layers were exfoliated and randomly dispersed into the PEN matrix. Mechanical and barrier properties of the fabricated nanocomposites performed by dynamic mechanical analysis and permeability analysis show significant improvements in the storage modulus and water permeability when compared to neat PEN. Differential scanning calorimeter (DSC) was used to investigate the isothermal crystallization behavior and melting behavior of PLSNs. DSC isothermal results revealed that the crystal growth process of PEN and PLSNs are a three-dimensional spherulitic growth. The activation energy of PEN increases with increasing content of layered silicates. The result indicates that the addition of layered silicate into PEN reduces the transportation ability of polymer chains during crystallization processes.     

Exfoliation of layered silicate facilitated by ring-opening reaction of cyclic oligomers in PET-clay nanocomposites

Ethylene terephthalate cyclic oligomers (ETCs) have been successfully polymerized to a high molecular weight poly(ethylene terephthalate) (PET) employing the advantages of the low viscosity of cyclic oligomers and lack of chemical emissions during polymerization. Using ring-opening polymerization of ETCs with organically modified montmorillonite (OMMT), we intend to ascertain the possibility of preparing high performance PET/clay nanocomposites. Due to the low molecular weight and viscosity, ETCs are successfully intercalated to the clay gallerys, what is evidenced by XRD showing a down-shift of basal plane peak of layered silicate along with TEM investigation. Subsequent ring-opening polymerization of ETCs in-between silicate layers yielded a PET matrix of high molecular weight along with high disruption of layered silicate structure and homogeneous dispersion of the latter in the matrix. Although co-existence of exfoliation and intercalation states of silicate layers after polymerization of ETCs rather than perfect exfoliation was observed, a dramatic increase in d-spacing along with fast polymerization presents us a great potential of cyclic oligomer process in producing a thermoplastic polymer-clay nanocomposites of extremely well-dispersed silicate nanoplatelets and the corresponding high performances.     

Preparation and characterization of transparent ZnO/epoxy nanocomposites with high-UV shielding efficiency

Transparent ZnO/epoxy nanocomposites with high-UV shielding efficiency were reported in this paper. First, zinc oxide (ZnO) precursor was synthesized via the homogeneous precipitation method and ZnO nanoparticles were then made by calcination of the precursor at different temperature. The structural properties of the as-prepared ZnO nanoparticles were studied in detail using thermogravimetry (TGA), differential thermal analysis (DTA), X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR) and transmission electron microscopy (TEM), respectively. Transparent ZnO/epoxy nanocomposites were subsequently prepared from transparent epoxy (EP-400) and as-prepared ZnO nanoparticles via in situ polymerization. Optical properties of ZnO/epoxy nanocomposites, namely visible light transparency and UV light shielding efficiency, were studied using an ultraviolet-visible (UV-vis) spectrophotometer. The optical properties of the as-obtained nanocomposites were shown to depend on ZnO particle size and content. The nanocomposite containing a very low content (0.07% in weight) of ZnO nanoparticles with an average particle size of 26.7 nm after calcination at 350 °C possessed the most optimal optical properties, namely high-visible light transparency and high-UV light shielding efficiency, that are desirable for many important applications.     

Synthesis and characterization of resol‐layered silicate nanocomposites

Resol‐layered silicate nanocomposites were synthesized by intercalative polymerization of phenol and formaldehyde using layered clays such as an aminoacid‐modified montmorillonite (MMT) and a commercial modified MMT (Cloisite 30B). The composites were prepared by a sequential process in which one of the reactives of the phenolic resin was reacted with the organosilicate and subsequently cured with triethylamine. The nanocomposites were studied by means of X‐ray diffraction, atomic force microscopy, and thermogravimetric analysis. Results show a strong clay composition dependence on the intercalation state. The composite of resol with 2 wt % aminoacid‐modified MMT content has the best dispersion of clay layers. Thermal stability of nanocomposites was slightly increased in comparison with the neat resol. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation of different dendritic‐layered silicate nanocomposites

Several dendrimer–clay nanocomposites have been prepared. Firstly, the dendrimer (DE₁)/clay nanocomposite was obtained via an in situ free radical polymerization of a double bond‐ended dendrimer (DE₁), derived from Behera's amine by using 2,2′‐azobisisobutyronitrile (AIBN), as initiator, and Cloisite 30 B, as nanofiller. Further free radical in situ copolymerization processes were conducted between DE₁, methyl methacrylate (MMA), and styrene (St). Two other dendrimer/clay nanocomposites were prepared by the reaction of second generation (G₂)–36‐acid dendrimer (DE₂) and N,N′,N′,N′‐tetrakis[2‐hydroxy‐1,1‐bis(hydroxylmethyl) ethyl]‐α,α,ω,ω‐alkane‐tetracarboxamide [6]‐10‐[6] Arborols (DE₃) with montmorillonite clay (MMT). POLYM. ENG. SCI., 53:2166–2174, 2013. © 2013 Society of Plastics Engineers     

Preparation of dendritic adamantane‐based polymers/layered silicate nanocomposites

An adamantane‐based atom transfer radical initiator (Adm‐Br) was prepared by the treatment of 1‐[[N‐[2‐Hydroxy‐l,l‐bis(hydroxymethyl)ethyl]amino]carbonyl]adamantane with bromopropionyl bromide. The resulting initiator was subsequently used in the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) to form (Adm‐p‐MMA), which was successfully used, as a macroinitiator, in further ATRP reactions with 3‐O‐methacryloyl‐1,2 5,6‐di‐O‐isopropylidene‐α‐d ‐glucofuranose (gly), a glycomonomer, to afford the Adm‐p‐MMA‐b‐gly polymer. The new Adm‐p‐MMA‐b‐gly polymer subsequently was employed to form a nanocomposite with chitosan‐modified, Nanofil clay (NC). The resulting Adm‐p‐MMA‐b‐gly/NC composite material was progressively hydrolyzed to regenerate the OH groups of the glucose units within the Adm‐p‐MMA‐b‐gly copolymer. The polymer/NC nanocomposites were characterized by X‐ray diffraction, thermal gravimetric analysis, differential scanning calorimetry, and transmission electron microscopy. POLYM. ENG. SCI., 54:2669–2675, 2014. © 2013 Society of Plastics Engineers     

层状硅酸盐／橡胶纳米复合材料（一）：用熔融插层法提高层状硅酸盐／天然橡胶纳米复合材料的工艺和加工性能

天然橡胶纳米复合材料是通过天然橡胶与有机改性的硅酸盐熔融复合制备的。该研究亦对比使用了未有机化的原始层状硅酸盐和非层状硅酸盐（EIC）。所用的层状硅酸盐是钠皂土（BNT）；而所用的有机粘土则是以十八烷基铵类改性的蒙脱土（MMT-ODA）和以甲基牛脂基双（2-羟乙基）季铵类改性的蒙脱土（MMT-TMDA）。采用加有促进剂的硫黄硫化体系进行硫化。借助X-射线衍射和透射电子显微镜研究这些硅酸盐的分散。加入有机粘土的纳米复合材料显示出较快的硫化速度和提高了的物理机械性能。复合材料的物理机械性能提高度按如下顺序排列：MMT-ODA〉MMT-TMDA〉EIC〉BNT。这种性能的提高归因于有机硅酸盐的插层／剥离，而硅酸盐的插层／剥离行为又是因其层内间距较大所致。     

Preparation and characterization of polyimide/modified layered double hydroxide nanocomposites

Polyimide (PI)/modified layered double hydroxide (m‐LDH) nanocomposites were prepared in this study. For this work, m‐LDHs were prepared from layered double hydroxides (LDHs) through an anionic exchange reaction with pyromellitic dianhydride (PMDA), succinic acid or terephthalic acid. PMDA and 4,4′‐oxydianiline were used to make the poly(amic acid) precursor for PI. X‐ray diffraction and transmission electron microscopy measurements confirmed that the PMDA‐modified LDH (PMH) and terephthalic acid‐modified LDH (TMH) were well dispersed in the PI matrix. For the succinic acid‐modified LDH, some of the LDH was intercalated with the succinic acid molecules but most maintained its original structure. Thus, the PI/PMH and PI/TMH nanocomposites exhibited improved mechanical, thermal and electrical properties compared to pure PI. The PMH has aromatic groups and is expected to have better π–π interactions with the PI chains than the other m‐LDHs. Thus, the PI/PMH nanocomposites exhibited the best properties among the nanocomposites investigated. Copyright © 2010 Society of Chemical Industry     

Preparation, characterization and antimicrobial activity of quaternized carboxymethyl chitosan and application as pulp-cap

Quaternized carboxymethyl chitosan (QCMC) was prepared from which carboxymethyl chitosan (CMC) was prepared from chitosan first, then N-quaternary ammonium group was introduced by the reaction of CMC with 2, 3-epoxypropyl trimethylammonium. The structures of the derivatives were characterized by FT-IR, XRD, ¹³C NMR, ¹H NMR and gel permeation chromatography. In vitro antimicrobial activities of QCMC were evaluated against Escherichia coli, which is a Gram-negative bacterium, and Staphylococcus aureus, which is a Gram-positive bacterium. In compared with carboxymethyl chitosan (CMC) and quarternary chitosan (QC) of the same degree of substitusion (DS), we found that QCMC has stronger antimicrobial activity. Then we went deep into study of the relationship between their structure and antimicrobial activity, found that the DS of CMC do little effect to their antimicrobial activity, but as the increase of their DS of quaternization or the decrease of their molecular weight, the antimicrobial activity of QCMC become stronger. QCMC was complexed with calcium hydroxide as pulp-cap. Animal experiment results indicated that QCMC can strongly induce reparative dentine formation and showed a better ability in dentin inducing compared with calcium hydroxide.     

Aliphatic polyamidoamine hyperbranched polymers/layered silicate nanocomposites

Polyamidoamine hyperbranched polymer (Hyp)/clay nanocomposites were synthesized by using both of montmorillonite and laponite clays. Poly amidoamine hyperbranched polymer (Hyp) was prepared by one‐pot polymerization via couple monomer methodology. Afterward, the amino ends of Hyp were modified with methyl methacrylate (MMA), styrene (St) and butyl methacrylate (n‐BuMA) polymers which were previously prepared via ATRP (atom transfer radical polymerization) to form the corresponding new hyperbranched polymers Hyp₁, Hyp₂ and Hyp₃. Those formed polymers were inserted into the modified clay, such as montmorillonite and laponite to form their nanocomposites. The formed polymer/clay nanocomposites were characterized via XRD, TEM, and thermal analyses. The formed hyperbranched polymers generally showed intercalation behavior more than the exfoliation one mostly because of the bulkiness of the hyperbranched skeleton. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Tensile properties of polyethylene-layered silicate nanocomposites

The sodium ions of clays with different cation exchange capacities (CEC) have been exchanged with alkyl ammonium ions, in which 1-4 octadecyl chains are attached to the nitrogen atom. Due to the different cation cross-sectional area to available area per cation ratio, the resulting organo-montmorillonites (OMs) have different organic surface coverage and alkyl chain packing density. Nanocomposites of these OMs and HDPE were prepared and the influence of the organic monolayer structure on the exfoliation of montmorillonite and the tensile properties of the composites was studied. A high cation cross-sectional area to available area ratio led to complete surface coverage and large d-spacing, favoring the dispersion of the filler. In spite of the identical chemical structure of the polymer and the organic monolayer, complete exfoliation was not attained. Partial exfoliation was achieved without a compatiblizer, which often adversely affect the mechanical properties of the composites. Enhanced exfoliation increased the elastic modulus and yield stress but decreased the yield strain and stress at break of the nanocomposites. Increased filler loading enhanced the elastic modulus but decreased all other tensile properties. The tensile properties were correlated to the volume fraction of the inorganic part of the OMs and not to the total volume of the OM. Fitting the elastic modulus data to the Halpin-Tsai equation showed that the fitting parameter in this equation is not only related to the aspect ratio of the inclusions.     

Preparation and flame resistance properties of revolutionary self-extinguishing epoxy nanocomposites based on layered double hydroxides

Layered double hydroxides/epoxy (LDHs/EP) nanocomposites were prepared from organo-modified LDHs, a diglycidyl ether of bisphenol A monomer (DGEBA) and amine curing agents. The organo-modified LDHs were obtained by ionic exchange of a magnesium-aluminum carbonate LDH in an acid medium. X-ray diffraction and transmission electron microscopy showed a dispersion of the layers at a nanometer scale, indicating the formation of LDH/EP nanocomposites. The thermal degradation and flame resistance properties of LDH/EP nanocomposites, montmorillonite-epoxy (MMT/EP) nanocomposites, LDH/EP microcomposites and aluminum hydroxide-epoxy microcomposites were compared by thermogravimetrical analyses, simultaneous thermal analyses, UL94 and cone calorimeter tests. Only LDH/EP nanocomposites showed self-extinguishing behavior in the horizontal UL94 test; LDH/EP microcomposites and MMT/EP nanocomposites samples burned completely showing that the unique flame resistance of LDH/EP nanocomposites is related to both the level of dispersion and the intrinsic properties of LDH clay. Furthermore, cone calorimeter revealed intumescent behavior for LDH/EP nanocomposites and a higher reduction in the peak heat release rate compared to MMT/EP nanocomposites.     

Preparation and combustion behaviour of polymer/layered silicate nanocomposites based upon PE and EVA

Polymer composites based on organically modified clay (organoclay) and polyethylene (PE) were prepared by melt processing to study their combustion behaviour. Formation of intercalated nanocomposites was observed only in presence of poly(ethylene-co-vinylacetate), added as a compatibilizer. The nanocomposite showed a reduced rate of combustion due to the accumulation of the silicate on the surface of the burning specimen which create a protective barrier to heat and mass transfer.