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.     

Impact of filler geometry and surface chemistry on the degree of reinforcement and thermal stability of nitrile rubber nanocomposites

The morphological, mechanical, and thermal stability of Nitrile rubber nanocomposites reinforced with fillers such as layered silicate (LS), calcium phosphate (CP) and titanium dioxide (TO) having different particle size and chemical nature were analyzed. The results revealed that the filler geometry played an important role on the mechanical and thermal stability of the composites. Calcium phosphate and titanium dioxide filled systems showed comparatively better mechanical and thermal stability compared to neat rubber. The activation energy needed for the thermal degradation was found to be higher for layered silicate filled system. DSC (Differential Scanning Calorimetry) analysis revealed a change in the T_g values as a result of the addition of fillers. This was more prominent with the case of layered silicate filler addition in comparison with calcium phosphate and titanium dioxide. The heat capacity values of the nanocomposites were carefully evaluated. The (∆Cp) with values obtained for different nanocomposites were correlated with the degree of reinforcement. It can be assumed that more polymer chains are attached on to the surface of the filler and there exists an immobilized layer around the filler surface and the layers do not take part in the relaxation process. The FTIR spectrum of the different samples highlighted the possible filler matrix interaction. The filler dispersion and aggregation in the polymer matrix were analyzed using X-ray diffraction studies (XRD), transmission electron microscopy (TEM), and atomic force microscopy (AFM).     

Structure and properties of organoclay/EPDM nanocomposites: Influence of ethylene contents

Four organoclay (OC)/ethylene–propylene–diene rubber (EPDM) nanocomposites with different ethylene contents were prepared by melt blending. X‐ray diffraction spectrum (XRD) and transmission electronic microscope (TEM) photos showed that OC/EPDM nanocomposites were intercalated, and the ethylene content had little influence on the dispersion of OC. The addition of OC prolonged the optimum cure time and reduced the crosslink density of OC/EPDM. The improvement in tensile strength of OC/EPDM nanocomposites with high ethylene contents (67–70%) was larger than that of OC/EPDM nanocomposites with low ethylene contents (52–52.5%). XRD results of the stretched samples testified that the extension promoted orientation of silicate layers, and induced crystallization of polyethylene (PE) segments in OC/EPDM nanocomposites with high ethylene contents. The highly oriented micro‐fibrillar structure and more oriented amorphous chains, which resulted from strain‐induced crystallization of PE segments and the orientation of clay layers in OC/EPDM nanocomposites with high ethylene contents (67–70%), should be responsible for larger improvement in tensile strength than that of those nanocomposites with low ethylene contents (52–52.5%) © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 914–919, 2006     

Organoclay Filled Natural Rubber Nanocomposites: The Effects of Filler Loading

Organoclay filled natural rubber (NR) nanocomposites were prepared using a laboratory two-roll mill. The effect of organoclay loading up to 10 phr was studied. The vulcanized nanocomposites were subjected to mechanical, thermal, and swelling tests. The results indicated that the tensile strength and elongation at break reached optimum at 4 phr of organoclay loading, and the incorporation of organoclay increased the tensile modulus and hardness of NR nanocomposites. The thermal degradation was shifted to a higher temperature and the weight loss decreased with incorporation of organoclay. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were employed to characterize the microstructure of NR nanocomposites. Results from TEM and XRD show the formation of intercalated and exfoliated individual silicate layers of organoclay filled NR nanocomposites particularly at low filler loading (< 4 phr).     

Biodegradable polyester layered silicate nanocomposites based on poly(ϵ‐caprolactone)

Nanocomposites based on biodegradable poly(?‐caprolactone) (PCL) and layered silicates (montmorillonite, MMT) were prepared either by melt interaction with PCL or by in situ ring‐opening polymerization of ?‐caprolactone as promoted by the so‐called coordination‐insertion mechanism. Both non‐modified clays (Na⁺ ‐MMT) and silicates modified by various alkylammonium cations were studied. Mechanical and thermal properties were examined by tensile testing and thermogravimetric analysis. Even at a filler content as low as 3 wt% of inorganic layered silicate, the PCL‐layered silicate nanocomposites exhibited improved mechanical properties (higher Young's modulus) and increased thermal stability as well as enhanced flame retardant characteristics as a result of a charring effect. It was shown that the formation of PCL‐based nanocomposites depended not only on the nature of the ammonium cation and related functionality but also on the selected synthetic route, melt intercalation vs. in situ intercalative polymerization. Interestingly enough, when the intercalative polymerization of ?‐caprolactone was carried out in the presence of MMT organo‐modified with ammonium cations bearing hydroxyl functions, nanocomposites with much improved mechanical properties were recovered. Those hybrid polyester layered silicate nanocomposites were characterized by a covalent bonding between the polyester chains and the clay organo‐surface as a result of the polymerization mechanism, which was actually initiated from the surface hydroxyl functions adequately activated by selected tin (II) or tin (IV) catalysts.     

Effect of amphiphilic compatibilizers on the filler dispersion and properties of polyethylene—thermally reduced graphene nanocomposites

Compatibilizers of different chemical structures and specifications were used to enhance the filler exfoliation in nanocomposites of polyethylene and thermally reduced graphene prepared by melt mixing route. The mechanical performance of the compatibilized nanocomposites was observed to be better than PE/G nanocomposites due to enhanced extent of filler exfoliation and distribution. Highest increase of 45% in tensile modulus and 13% in peak stress was observed in the composites. Overall, from the mechanical, rheological, thermal, and calorimetric properties, the compatibilizers with best performance were ethylene acrylic acid (EAA) copolymer and chlorinated polyethylene (CPE25). Furthermore, the extent of filler exfoliation was observed to increase with increasing EAA content thus confirming positive interactions between EAA and thermally reduced graphene, though no specific chemical interactions could be detected. The composite properties were observed to reach maximum around 7.5 wt % EAA content, followed by reduced performance due to extensive matrix plasticization. The observed behaviors were a result of interplay of opposing factors like filler exfoliation due to compatibilizer addition and matrix plasticization due to its lower molecular weight, thus the observed optimum comaptibilizer amount was specific to the compatibilizer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42484.     

Preparation and properties of new EPDM/vermiculite nanocomposites

Novel nanocomposites based on ethylene‐propylene‐diene rubber (EPDM) and maleic anhydride‐modified vermiculite (VMT) were prepared. Maleic anhydride (MA) acts both as the intercalation agent for VMT and as a vulcanizing agent for EPDM matrix. It also acts as a compatibilizer for EPDM and VMT phases. From analysis by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), the silicate layers of the VMT were exfoliated and dispersed uniformly in the EPDM matrix as monolayers. The thermal properties of the nanocomposites were investigated by dynamic mechanical thermal analysis and thermogravimetric analysis; a strong rubber‐filler interaction in the nanocomposites was manifested in the measured temperature range by the result of storage modulus. At the same time, there was some enhancement in degradation behavior between the nanocomposites and EPDM matrix. The nanocomposites exhibited a great improvement in tensile strength and modulus, as well as elongation at break. Finally, the effects of MA addition on the formation of nanometric reinforcement and on the mechanical properties of nanocomposites are discussed. POLYM. COMPOS., 26:706–712, 2005. © 2005 Society of Plastics Engineers     

Preparation and characterization of polymer/organosilicate nanocomposites based on unmodified LDPE

Low‐density polyethylene (LDPE)/silicate nanocomposites were prepared by the melt compounding and solution blend methods using unmodified LDPE polymer and layered silicates with different aspect ratio. X‐ray diffraction (XRD) analysis performed on composites obtained by dispersing the organosilicates in molten LDPE evidenced an exfoliated or partially exfoliated structure for the low aspect ratio silicate (laponite) in contrast to the high aspect ratio silicate (montmorillonite), which led to the formation of intercalated nanocomposites. With regard to the preparation method, the melt compounding method was more effective in forming exfoliated/highly intercalated LDPE nanocomposites compared with the solution blend method (using CCl₄ as a solvent). A gradual increase in crystallization temperatures (T_c) with increasing laponite content for LDPE‐organolaponite nanocomposites was revealed by differential scanning calorimetry (DSC) measurements. Thermogravimetric analysis and tensile measurements results indicated that thermal stability and elastic modulus increment were more prevalent for nanocomposites prepared using organomontmorillonite as filler. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of polyester-based nanocomposites coatings for automotive pre-coated metal

Polyester-based nanocomposites coatings were synthesized by the in situ polymerization with high speed homogenizer process at the various contents of organic modified montmorillonite (OMMT) to disperse into the polyester matrix. The dispersion state of organoclay was examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The absence of reflection pattern of organoclay and TEM study revealed that organoclay was partially intercalated and exfoliated into the polymer matrix. Mechanical property of polyester-based nanocomposites coatings (PE/OMMT) improved the tensile strength and good formability at the deep drawing test. The viscoelastic behavior of PE/OMMT nanocomposites coatings was observed by dynamic mechanical analysis (DMA). When the content of organoclay was increased, the stiffness of the PE/OMMT nanocomposites coatings increased considerably and T_g of each cured coatings shifted to a lower temperature. Anti-corrosion property was examined by the salt spray test. CNC-3 had little rust after 600 h and it implies that nano-sized layered silicate of organoclay effectively increases the length of the diffusion pathways water molecules. And nano-sized layered silicate of organoclay might be decreased the permeability and could make higher corrosion resistance of PE/OMMT nanocomposites coatings. From those results, CNC-3 had good formability in the deep drawing and also had good anti-corrosion property. So, CNC-3 would be an appropriate coating for automotive pre-coated metal.     

Effect of different preparation routes on the structure and properties of rigid polyurethane‐layered silicate nanocomposites

To identify the effect of reactive preparation on the structure and properties of rigid polyurethane (PU)‐layered silicate nanocomposite, a range of nanocomposites were prepared by combining the various precursors in different sequences. The morphology of the samples was characterized by XRD and TEM. Tensile properties and dynamic mechanical thermal properties were measured. The reactions between the layered silicates and PU precursors were monitored via FTIR to gain an understanding of the participation of nanofiller in the polymerization reaction, and the impact of this on system stoichiometry. The XRD and TEM results provided evidence that morphology can differ significantly if different synthesis methods are used. However, the mechanical properties are dominated by the stoichiometry imbalance induced by the addition of the layered silicates. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2894–2903, 2006     

Effect of matrix molecular weight on the dispersion of nanoclay in unmodified high density polyethylene

The effect that polymer molecular weight has on the dispersion of relatively polar montmorillonite (MMT) in nonpolar, unmodified high density polyethylene (HDPE) was examined. Polymer layered silicate (PLS) nanocomposites were prepared via melt compounding in a single screw extruder using three unmodified HDPE matrices of differing molecular weight and organically modified MMT (organoclay) in concentrations ranging from 2 to 8 wt%. The weight average molecular weights (M _W) of the HDPE matrices used ranged from 87,000 to 460,000 g/mol. X‐ray diffraction (XRD), tensile testing, dynamic mechanical thermal analysis (DMTA), and dynamic rheometry were performed on these nanocomposites. Nanocomposites generated from the high molecular weight (HMW) HDPE matrix exhibited increased intercalation of the MMT as shown by XRD and greater improvements in the Young's modulus when compared with nanocomposites generated from the low (LMW) and middle molecular weight (MMW) matrices. DMTA measurements carried out in torsion showed that the increase in shear modulus of the HMW nanocomposites was not as great as that of the LMW and MMW counterparts as observed from a lower percentage enhancement in the storage modulus (G′) and estimated heat distortion temperature (HDT). This was attributed to the higher degree of mechanical anisotropy in the HMW nanocomposites. POLYM. COMPOS., 28:499–511, 2007. © 2007 Society of Plastics Engineers     

宽峰聚乙烯／蒙脱土纳米复合材料的制备

利用2种不同的方法制备了2种氢调敏感性不同的蒙脱土／氯化镁／四氯化钛（MMT／MgCl2／TiCl4）催化剂,利用这2种催化剂及其混配催化剂,通过原位聚合法,制备出一系列宽峰聚乙烯纳米复合材料,采用X_射线衍射仪（XRD）、凝胶色谱测试分析（GPC）及力学性能测试等方法对催化剂及聚合产物进行分析,结果表明,2种催化剂以及按照不同比例混合的混配催化剂均表现出较高的聚合活性,XRD测试结果表明,蒙脱土片层在乙烯聚合过程中发生了插层及剥离,以单片层或几层共存的形式分散于聚乙烯基质中;用混配催化剂可制得宽峰聚乙烯纳米复合材料,Mw／Mn=7．23,并且聚合物的堆积密度达到工业生产的标准,宽峰聚乙烯纳米复合材料的综合力学性能较工业产品5000S及工业上应用的管材料有很大的提高。     

Ethylene vinyl acetate/Mg‐Al LDH nanocomposites by solution blending

Partially exfoliated ethylene vinyl acetate (EVA‐40, 40% vinyl acetate content)/layered double hydroxide (LDH) nanocomposites using organically modified layered double hydroxide (DS‐LDH) have been synthesized by solution intercalation method. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) studies of nanocomposites shows the formation of exfoliated LDH nanolayers in EVA‐40 matrix at lower DS‐LDH contents and partially intercalated/exfoliated EVA‐40/MgAl LDH nanocomposites at higher DS‐LDH contents. These EVA‐40/MgAl LDH nanocomposites demonstrate a significant improvement in tensile strength and elongation at break for 3 wt% of DS‐LDH filler loading compare to neat EVA‐40 matrix. Thermogravimetric analysis also shows that the thermal stability of the nanocomposites increases with DS‐LDH content in EVA‐40. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

PE/Clay Nanocomposite with Bimodal Molecular Weight Distribution Produced Via In-Situ Polymerization

A Ti-based Ziegler–Natta catalyst supported on the clay was used for producing the polyethylene/clay nanocomposites through in situ polymerization. This catalyst showed high activity in the ethylene polymerization. The two-step polymerization approach, i.e. in the presence and absence of hydrogen, was laid out to broaden the molecular weight distribution of the polyethylene/clay nanocomposite. The molecular weights and molecular weight distribution of the nanocomposites were characterized by the gel permeation chromatography. It was found that the molecular weight distribution was remarkably widened towards bimodal distribution by using the above mentioned approach. The thermal properties of the produced nanocomposites were studied by differential scanning calorimetry and thermal gravimetric analysis. The microstructure of the resulting bimodal polyethylene/clay nanocomposite was investigated by X-ray diffraction and transmission electron microscopy. The thermal gravimetric analysis indicated an improved thermal stability of the produced nanocomposites. In addition, the studies proved the nanocomposite formation with the exfoliated structure of the clay in the polyethylene matrix.     

Synthesize of polymer–silicate nanocomposites by in situ metal‐catalyzed living radical polymerization

Polymer–silicate nanocomposites were synthesized with atom transfer radical polymerization (ATRP). An ATRP initiator, consisting of a quaternary ammonium salt moiety and an α‐phenyl chloroacetyl chloride moiety, were intercalated into the interlayer spacings of the layered silicate. Subsequent ATRP of styrene with CuCl/2,2′‐bipyridine (bipy) as the catalyst with the initiator‐modified silicate afforded homopolymers with predictable molecular weights and low polydispersities, both characteristics of living radical polymerization. The polystyrene nanocomposites contained both intercalated and exfoliated silicate structures. The prepared materials were characterized by XRD, SEM, TEM, FTIR, and ¹H NMR techniques. Effect of silicate on thermal properties and glass transition temperature of polystyrene was investigated using thermogravimetric analysis and differential scanning calorimetric techniques. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Rubber/LDH nanocomposites by solution blending

The rubber nanocomposites containing ethylene vinyl acetate (EVA) having 60 wt % of vinyl acetate content and organomodified layered double hydroxide (DS‐LDH) as nanofiller have been prepared by solution intercalation method and characterized. The XRD and TEM analysis demonstrate the formation of completely exfoliated EVA/DS‐LDH nanocomposites for 1 wt % filler loading followed by partially exfoliated structure for 5–8 wt % of DS‐LDH content. EVA/DS‐LDH nanocomposites show improved mechanical properties such as tensile strength (TS) and elongation at break (EB) in comparison with neat EVA. The maximum value of TS (5.1 MPa) is noted for 3 wt % of DS‐LDH content with respect to TS value of pure EVA (2.6 MPa). The data from thermogravimetric analysis show the improvement in thermal stability of the nanocomposites by ≈15°C with respect to neat EVA. Limiting oxygen index measurements show that the nanocomposites act as good flame retardant materials. Swelling property analysis shows improved solvent resistance behavior of the nanocomposites (1, 3, and 5 wt % DS‐LDH content) compared with neat EVA‐60. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Experimental investigation on the influence of the composition on the morphology and the mechanical properties of short glass fiber‐reinforced polypropylene nanocomposites

Polypropylene composites containing 0–5 wt% layered silicate and 0–30 wt% short glass fibers are prepared by melt compounding. To investigate the influence of different compositions on the mechanical properties of short glass fiber‐reinforced polypropylene nanocomposites, materials with various filler contents are prepared. At a glass fiber content of 10 wt% Young's modulus of the layered silicate‐containing composites decreases by around 30% compared to conventional glass fiber‐reinforced polypropylene. But at higher glass fiber loadings, an increasing modulus of up to 10% is observed. However, the addition of layered silicate results in large decreases of the tensile and the notched impact strength. A maleic anhydride‐grafted polypropylene enhances Young's modulus and the tensile strength. © 2012 Society of Plastics Engineers     

The effect of polyoxypropylene‐montmorillonite intercalates on polymethylmethacrylate

Polymethylmethacrylate (PMMA)‐layered silicate nanocomposites have been prepared by in situ polymerization of commercial type of methylmethacrylate monomer (MMA), for denture base material, into organoclay. Organoclay was prepared through an ion exchange process between sodium cations in montmorillonite and NH₃⁺ groups in polyethertriamine hydrochloride and polyoxypropylene triamine hydrochloride with different molecular weight (5000, 440). X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) have been used to investigate the structure of the resulting composites. Both intercalated and exfoliated nanocomposites were obtained depending on the type and amount of organoclay. The thermal decomposition temperatures of the nanocomposites were found to be higher than that of pristine polymer. PMMA was strongly fixed to inorganic surfaces, due to cooperative formation of electrostatic bonding between NH₃⁺ group and negatively charged surface of layered silicate and amide linkage between PMMA and polyethertriamine or polyoxypropylene triamine. The effect of the organoclay on the hardness, toughness, tensile stress, and elongation at break of the polymer was studied and was compared with pristine polymer. The hardness and Izod impact strength of PMMA‐organoclay nanocomposites were enhanced with the inclusion of clay. Tensile properties appear to be enhanced at certain organoclay content. However, the water absorption is slightly higher than the pristine PMMA. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Effect of layered silicate on EPDM/EVA blend nanocomposite: Dynamic mechanical,thermal, and swelling properties

Polymer blend nanocomposites have been developed by solution method using ethylene propylene diene terpolymer (EPDM), ethylene vinyl acetate (EVA‐45) copolymer, and organically modified layered silicate. Morphological investigation made by wide‐angle X‐ray diffraction and transmission electron microscopic analysis indicates intercalated structure of EPDM/EVA nanocomposites with partial disorder. Scanning electron microscopic studies exhibit the phase behavior of EPDM/EVA blend nanocomposites. Dynamic mechanical thermal analysis shows a significant increase in storage modulus in the rubbery plateau. The decrease in damping (tan δ) value and enhanced glass‐transition temperature (T_g) demonstrate the reinforcing effect of layered silicate in the EPDM/EVA blend matrix. The tensile modulus of these nanocomposites also showed a significant improvement with the filler content. The main chain scission of EPDM/EVA blend nanocomposites compared with the neat EPDM/EVA blend showed substantial improvement in thermal stability in nitrogen, whereas a sizeable increase is observed in air. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Poly(butylene sucinate-co-adipate)/montmorillonite nanocomposites: effect of organic modifier miscibility on structure, properties, and viscoelasticity

Poly(butylene succinate-co-adipate) (PBSA)/layered silicate nanocomposites were prepared by melt extrusion of PBSA and three different types of commercially available organically modified montmorillonite (OMMT). Using three types of OMMT modified with three different kinds of surfactants, the effect of organic modification on nanocomposites was investigated by focusing of three major aspects: morphological study, property measurements, and melt rheological behavior under both small and large deformation flows. X-ray diffraction (XRD) patterns revealed that increasing the level of interactions (miscibility) between the organic modifier and PBSA matrix increases the tendency of the silicate layers to delaminate and distributed nicely within the PBSA matrix. Transmission electron micrographic (TEM) observations showed that the ordering of silicate layers in PBSA matrix is well matched with the XRD patterns. Thermal analysis revealed that extent of crystallinity of PBSA matrix is directly related to the extent of exfoliation of silicate layers in the nanocomposites. Dynamic mechanical analysis and tensile property measurements showed concurrent improvement in mechanical properties when compared to the neat PBSA and the extent of improvement is directly related to the extent of delamination of silicate layers in the PBSA matrix. The same tendency was also observed in melt rheological measurements.