STRUCTURAL EVOLUTION AND COMPOSITION CHANGE IN THE SURFACE REGION OF POLYPROPYLENE/CLAY NANOCOMPOSITES ANNEALED AT HIGH TEMPERATURES

A model experiment was done to clear the formation mechanism of protective layers during combustion of polypropylene(PP)/organically modified montmorillonite(OMMT) nanocomposites.The investigation was focused on the effects of annealing temperature on the structural changes and protective layer formation.The decomposition of OMMT and degradation of PP/OMMT nanocomposites were characterized by means of thermogravimetric analysis(TGA).The structural evolution and composition change in the surface region of PP...

PREPARATION OF POLYPROPYLENE/CLAY NANOCOMPOSITES BY in situ POLYMERIZATION WITH TiCl_4/MgCl_2/CLAY COMPOUND CATALYST

TiCl4/MgCl2/clay compound catalyst was prepared by chemical reaction. Exfoliated polypropylene （PP）/clay nanocomposites were synthesized by in situ polymerization with this compound catalyst. Effects of polymerization temperature, polymerization time, propylene pressure, solvent consumption and pre-treat time of catalyst on catalyst activity and catalytic stereospecificity were studied. Under optimal conditions, activity of the nano-compound catalyst is about 88.3 kg/（mol Ti-h）. Isotacticity of PP obtained in the nanocomposites is in the range of 89%-99%, and its melting temperature is about 159℃. The weight-average molecular weight of PP can reach 6.7 × 10^5 - 7.8 × 10^5, and the molecular weight distribution is between 7.7 and 7.9.

Fracture Toughness Studies of Polypropylene- Clay Nanocomposites and Glass Fibre Reinfoerced Polypropylene Composites

In this paper, a comparative study on the fracture toughness of woven glass fibre reinforced polypropylene, chopped glass fibre reinforced polypropylene and nanoclay filled polypropylene composites is presented. Nanoclays (Cloisite 15A) of 1 wt. % to 5 wt. % were filled in polypropylene (PP) matrix and they were subjected to fracture toughness stu-dies. The specimen with 5 wt. % nanoclay showed 1.75 times and 3 times improvement in critical stress intensity factor (KIC) and strain energy release rate (GIC), respectively, over virgin PP. On the other hand, 3 wt. % nanoclay PP composites showed superior crack containment properties. These structural changes of composite specimens were examined using Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD) methods. It showed that exfoli-ated nanocomposite structures were formed up to 3 wt. % nanoclay, whereas, intercalated nanocomposite structures formed above 3 wt. % nanoclay in the PP matrix. Furthermore, the woven fibre reinforced PP composites demonstrated superior crack resistant properties than that of clay filled nanocomposites and chopped fibre PP composites. However, KIC and GIC values for woven fibre composites were lesser than that of chopped fibre composites. Moreover, KIC and GIC values for both nanoclay filled PP composites and woven fibre composites are comparable even though the clay filled PP demonstrated catastrophic failure. Also, the crack propagation rate of PP-nanoclay composites is comparable to that of chopped fibre composites.

DISPERSION AND TENSILE BEHAVIOR OF POLYPROPYLENE/MONTMORILLONITE NANOCOMPOSITES PRODUCED VIA MELT INTERCALATION

Most of the articles on polymer nanocomposites focus on the importance of chemistry used to modify the surface of the clay, usually montmorillonite (MMT), and characterization of the nano-scale structure obtained. The role and importance of processing were also discussed recently. However, few papers concerning the correlation between morphology of MMT and mechanical properties were published. In order to understand. the tensile behavior of PP/Montmorillonite (MMT) nanocomposites better, and to further improve the reinforcement efficiency, we first prepared the PP nanocomposites via direct melt intercalation using conventional twin-screw extrusion. The dispersion and tensile property of the composites were then investigated by SEM, XRD, TEM and a video-controlled tensile set-up. The macroscopic and microscopic dispersion of MMT in PP matrix was verified by XRD and TEM, combined with SEM. The tensile properties were obtained by video-controlled tensile set-up, which gives true stress-strain curve. It was found that a partly intercalated and partly exfoliated structure (also called incomplete exfoliation) existed in the system. Though the tensile strength of PP nanocomposites is not much improved in engineering stress-strain curves, more than 20% increase of true stress was found in a true stress-strain experiment at high true strain, which indicates that only oriented silicate layers can have a big effect on tensile properties: Not only orientation of silicate platelets but also the degree of exfoliation is a key factor to determine the reinforcement efficiency. The reinforcement efficiency of MMT has been discussed based on the 'continuum' Halpin-Tsai equations. A good agreement was found between experimental data and theoretical prediction by changing N value (number of platelets per stack) which corresponding to different state of the dispersion of MMT in PP matrix.

Polycarbonate/Polypropylene/Fibrillar Silicate Ternary Nanocomposites via Two-step Blending Process: Degradation and Morphology

The method of two-step melt blending was used to prepare polycarbonate/polypropylene/attapulgite ternary nanocomposite, and the various techniques including gel permeation chromatography, rheometer, transmis- sion electron microscope, dynamic mechanical analysis were used to examine the degradation of polycarbonate (PC) and the nanocomposite morphology. The results showed that the molecular weight degradation of PC triggered by attapulgite (AT) during the direct blending process was inhibited effectively by using two-step melt blending, in which AT was blended with polypropylene (PP) prior to compound with PC. The morphology of encapsulation was formed in the PC matrix, where PP encapsulates AT fibrillar single crystals to form a core-shell inclusion. Dynamic mechanical analysis (DMA) measurements showed that the PC/PP/AT ternary nanocomposites were more effective than conventional PC/PP blends in reinforcement, meanwhile the addition of AT in the ternary nanocomposites shifted the glass transition temperature of the PP phase to a higher value.

Modification of Nanocomposites by Melting Intercalation of Polypropylene in Montmorillonite

The polypropylene wax modified by ultraviolet irradiation. The polypropylene-montmorillonite nanocomposiles were prepared by direct melting intercalation oj polypropylene powders. The structure of polypropylene , the polyproprlene irradiated, montmorillinote and polypropylene-montmorillonite composites were studied by XRD, 1R and DSC. The results show that the PP molecules can are oxidized during ultraviolet irradiation , melt polypropylene can intercalate into montmorillonite layer. As a result, the layered distance ( d0.01) of montmorillonite increases, and the melt absorption peak of polypropylene in layer is eliminated.

SYNTHESIS AND CHARACTERIZATION OF POLYPROPYLENE/MONTMORILLONITE NANOCOMPOSITES VIA AN in-situ POLYMERIZATION APPROACH

Polypropylene/montmorillonite (PP/MMT)nanocomposites were prepared by in-situ polymerization using aMMT/MgCl_2/TiCl_4-EB Ziegler-Natta catalyst activated by triethylaluminum(TEA). The enlarged layer spacing of MMT wasconfirmed by X-ray wide angle diffraction (WAXD), demonstrating that MMT were intercalated by the catalyst components.X-ray photoelectron spectrometry (XPS) analysis proved that TiCl_4 was mainly supported on MgCl_2 instead of on the surfaceof MMT The exfoliated structure of MMT layers in the PP matrix of PP/MMT composites was demonstrated by WAXDpatterns and transmission electron microscopy (TEM) observation. The higher glass transition temperature and higher storage modulus of the PP/MMT composites in comparison with pure PP were revealed by dynamic mechanical analysis (DMA).

STRUCTURING & RHEOLOGY OF MOLTEN POLYMER/CLAY NANOCOMPOSITES

The evolution and the origin of“solid-like state”in molten polymer/clay nanocomposites are studied.Usingpolypropylene/clay hybrid(PPCH)with sufficient maleic anhydride modified PP(PP-MA)as compatibilizer,well exfoliationyet solid-like state was achieved after annealing in molten state.Comprehensive linear viscoelasticity and non-lineartheological behaviors together with WAXD and TEM are studied on PPCH at various dispersion stages focusing on time,temperature and deformation dependencies of the“solid-like”state in molten nanocomposites.Based on these,it is revealedthat the solid-structure is developed gradually along with annealing through the stages of inter-layer expansion by PP-MA,the diffusion and association of exfoliated silicate platelets,the formation of band/chain structure and,finally,a percolatedclay associated network,which is responsible for the melt rigidity or solid-like state.The network will be broken down bymelt frozen/crystallization and weakened at large shear or strong flow and,even more surprisingly,may be disrupted by usingtrace amount of silane coupling agent which may block the edge interaction of platelets.The solid-like structure causescharacteristic non-linear rheological behaviors,e.g.residual stress after step shear,abnormal huge stress overshoots in stepflows and,most remarkably,the negative first normal stress functions in steady shear or step flows.The rheological andstructural arguments challenge the existing models of strengthened entangled polymer network by tethered polymer chainsconnecting clay particles or by chains in confined melts or frictional interaction among tactoids.A scheme of percolatednetworking of associated clay platelets,which may in band form of edge connecting exfoliated platelets,is suggested toexplain previous experimental results.

Study on Morphology and Mechanical Properties of High-functional Epoxy Based Clay Nanocomposites

Morphology and mechanical properties of clay/high-functional epoxy nanocomposites are investigated. An intercalated morphology is always observed for clay loadings ≤5 wt %. The glass transition temperature （Tg） of the composites decreases with the clay loading, and the impact strength increases first by 10% at 2 wt% clay loading, and is followed by a dramatic decline, while the flexural strength decreases in all cases.

Structure and Properties of Polyamide 11 Nanocomposites Filled with Fibrous Palygorskite Clay

Various amounts(up to 10 wt%)of palygorskite nanofibers functionalized by 3-aminopropyltriethoxysilane(APTES)coupling agent were used to reinforce polyamide 11 nanocomposites prepared by melt compounding.The covalent bonding of the silane on the palygorskite surface was confirmed by infrared spectroscopy and thermogravimetric analysis.X-ray diffraction revealed the retention of theα-form of polyamide crystals upon the addition of both natural and silane treated palygorskite nanorods.All the investigated nanocomposites showed an improvement of the thermal stability,especially when surface treated palygorskite nanofibers were considered.Tensile tests and dynamic mechanical thermal analyses on the prepared materials evidenced how the incorporation of palygorskite nanofibers significantly increased the elastic and the storage moduli of polyamide,and this enhancement was more evident when natural palygorskite nanorods were used.

Influence of clay concentration on the morphology and properties of clay-epoxy nanocomposites prepared by in-situ polymerization under ultrasonication

To investigate the effect of clay concentration on the structures and properties of bisphenol-A epoxy/nanoclay composites, three composites with organoclay concentrations of 2.5wt%, 5wt%, and 7.5wt% of the epoxy resin were prepared by in-situ polymerization under mechanical stirring followed by ultrasonic treatment. The clay aggregates on micro-scale indicate the absence of fully exfoliated nanocomposites. The layer space decreases with the increase of clay concentration, which suggests that the exfoliation would be constrained if more clay is added as the ultrasonic force is exerted. The thermal decomposition temperature remains almost unchanged with the increase of clay concentration. The glass transition temperature of the composites decreases slightly with the increase of clay concentration, whereas the storage modulus increases with the increase of clay concentration.

Effect of functionally-graded interphase on the elasto-plastic behavior of nylon-6/clay nanocomposites;a numerical study

In nanocomposites,the interphase thickness may be comparable to the size of nano-particles,and hence,the effect of interphase layers on the mechanical properties of nanocomposites may be substantial.The interphase thickness to the nano-particle size ratio and properties variability across the interphase thickness are the most important affecting parameters on the overall behavior of nanocomposites.In this study,the effect of properties variability across the interphase thickness on the overall elastic and elastoplastic properties of a polymeric clay nanocomposite(PCN)using a functionally graded(FG)interphase is investigated in detail.The results of the computational homogenization on the mesoscopic level show that Young’s modulus variation of the interphase has a significant effect on the overall elastic response of nanocomposites in a higher clay weight ratio(Wt).Moreover,strength variation through the interphase has a notable effect on the elasto-plastic properties of PCNs.Also,the increase or decrease in stiffness of interphase from clay to matrix and vice versa have a similar effect in the overall behavior of nanocomposites.

Effects of Synthetic and Processing Methods on Dispersion Characteristics of Nanoclay in Polypropylene Polymer Matrix Composites

This work presents the effect of synthetic procedures (extrusion and casting) on the dispersion characteristics of nano layered silicate clay particles in the polypropylene (PP) polymer matrix. Three different molecular weights PP samples are taken and filled with nanoclay of 1 wt% and 3 wt%, and these nanocomposites were synthesized by using an extrusion or casting methods. The X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) is used to characterize the structure and morphology of nanocomposites. Rheological and mechanical results show that the extruded products are better than that of cast products. The outcome of this work is discussed in this paper.

Using Image Analysis for Structural and Mechanical Cha-racterization of Nanoclay Reinforced Polypropylene Com-posites

This paper focuses on the micromechanical study of the tensile property of Polymer-Clay Nanocomposites (PCN). Polypropylene (PP) filled with nanoclay is chosen as the PCN. Measurements of optical dispersion parameters (as discussed by Basu et al., namely, exfoliation number (ξn), degree of dispersions (χ) and agglomerate %) in PCN system were carried out using Transmission Electron Microscopy (TEM) and Optical Microscopy (OM). The experimentally obtained tensile modulus is compared with theoretically obtained modulus values from the optical dispersion parameters and observed a close matching between these values. Also, the tensile values are compared with other standard theoretical models and observed that the results obtained from optical dispersion parameters are suited well with experimental results.

~2H-NMR CHARACTERIZATION OF CLAY DISPERSION AND CONFINEMENT EFFECT ON PROBE MOLECULES IN RUBBER/CLAY NANOCOMPOSITE-GELS

~2H-NMR spectroscopy of the probe molecule,deuterated benzene,was applied to characterize organo-clay dispersion and confinement effect on the local motion of benzene in rubber/clay nanocomposite-gels.The observed ~2H line shapes of benzene in intercalated and exfoliated nanocomposites were obviously different,which can be used to estimate clay-dispersion quality.~2H-NMR line shapes also reflect the different influence of intercalated or exfoliated layered-silicates on local motions of benzene,implying that...

Structure and properties of SEBS/PP/OMMT nanocomposites

Nanocomposites based on styrene-b-(ethylene-co-butylenes)-b-styrene triblock copolymer(SEBS), polypropylene (PP) and organomontmorillonite (OMMT) were prepared using melt intercalation by a twin mill. The nanostructure of SEBS/PP/OMMT hybrids was characterized by X-ray diffractometry(XRD) and transmission electron microscopy(TEM). The d001 space of OMMT and SEBS/PP/OMMT hybrid increases from 1.30 nm to 3.52 nm and 4.06 nm, respectively which indicate, that the C16 and SEBS/PP could intercalate in the silicate layers and expand the basal spacing. The formation of intercalated structure was also confirmed by TEM. The results show that the individual silicates are well dispersed in the elastomer matrix. The glass transition temperature (tg) of PS block of SEBS was investigated by dynamic mechanical analysis (DMA). It is shown that there are remarkable enhancements in tg of PS block containing a small mass fraction of OMMT. tg of PS in SEBS of the nanocomposites has been increased about 39℃when containing 4% OMMT. The influence of OMMT on the dynamic storage moduli is temperature dependent. Below 50℃the SEBS/PP/OMMT composites with higher OMMT contents show higher dynamic storage moduli. OMMT has the function of reinforcing SEBS/PP elastomers. However, the influence of OMMT on the mechanical properties of the nanocomposites is not significant according to the tensile test and tear test.

Nanocomposite Polymer Hydrogels Reinforced by Carbon Dots and Hectorite Clay

Herein, two nanoparticles with different dimensions, spherical carbon dots (C-dots) and sheetlike hectorite clay, were used as physical crosslinkers to fabricate C-dots-clay-poly(N-isopropylacrylamide)nanocompositehydrogels (coded as C-dots-clay-PNIPAm hydrogels). The mechanical properties, fluorescence features and thermal-responsive properties of the C-dots-clay-PNIPAm hydrogels were evaluated. The experimental results indicate that synergistic effects of C-dots and hectorite clay nanoparticles are able to significantly enhance mechanical properties of the hydrogels. The hydrogels can be stretched up to 1730%with strength as high as 250 kPa when the C-dots concentration is 0.1wt%and the clay concentration is 6wt%. The hydrogels exhibit complete self-healing through autonomic reconstruction of crosslinked network a damaged interface. The hydrogels show favorable thermal-responsive properties with the volume phase transition around 34℃. In addition, the hydrogels are endowed with fluorescence features that are associated with C-dots in the hydrogels. It can be expected that the as-fabricated C-dots-clay-PNIPAm hydrogels are promising for applications in sensors, biomedical carriers and tissue engineering.

Preparation and Properties of a New Type of Poly(butylene-terephthalate)with Layered Silicate Nanocomposites

In this paper, poly(butylene-terephthalate)-layered silicate of clay nanocomposites (NPBT) are reported. Their thermal properties, heat distortion temperature (HDT) and crystallization nucleation are investigated. NPBT samples have apparent viscosity over 0.85, HDT of 30℃ to 50℃ higher than that of poly (butylene-terephthalate) (PBT) for clay load from 1.0% to 10.0% (by mass), and higher capability to accommodate clay than other polymers. The nonisothermal crystallization experiments indicate that the better thermal degradation behavior and crystallization rate of NPBT are 50% higher than PBT, and its injection mould processing temperature is lowered from 110℃ to 55℃. NPBT samples are characterized by several techniques. X-ray shows an original clay interlayer distance enlarged from 1.0 nm to 2.5 nm, while both TBM and AFM indicate an average size from 30nm to lOOnm of exfoliated clay layers, and 3%(by mass) of particle agglomeration being phase separated from PBT matrix, which are factors on some mechanical properties decrease of NPBT. The disappearance of spherulitic morphology in NPBT resulted from layers nucleation is detected. Improving NPBT properties by treating clay with long chain organic reagent and controlling the way to load it is suggested.

PREPARATION AND PROPERTIES OF CLAY/POLY（N-ISOPROPYLACRYLAMIDE-co-A CRYL AMIDE） NANOCOMPOSITE HYDROGELS

A series of clay/poly（N-isopropylacrylamide-co-acrylamide） nanocomposite hydrogels （S-N-M gels） have been successfully prepared by in situ polymerization. The mechanical properties, swelling behavior of S-N-M gels and the transparency changes during polymerization of S-N-M gels have been systematically investigated. Compared to traditional hydrogels, S-N-M gels show excellent tensile properties and their swelling ratio increases with increasing acrylamide （AAm） content. The results of stress relaxation indicate that the stress loss decreases with increasing AAm content. It was surprisingly found that the transparency during all S-N-M gel synthesis changes abruptly, and the changes become more abrupt with increasing N-isopropylacrylamide content. It was concluded that the fact may be related to the hydrophilicity of copolymers. The weaker the hydrophilicity of copolymer, the more apparent the transparency change during S-N-M gels polymerization. We believe the relationship between hydrophilicity of copolymer and transparency changes will help to design novel nanocomposite hydrogels.

Crystallization Behavior and Thermal Properties of PP/MgAl LDH Nanocomposites Prepared in Non-polar Solution

Polypropylene（PP）/MgAl layered double hydroxide（MgAl LDH） nanocomposites were synthesized by refluxing PP and dodecyl sulfate-intercalated MgAI LDH[MgAI（DS）] in non-polar xylene. Their structure, thermal and crystallization properties were studied via X-ray diffraction（XRD）, transmission electron microscopy（TEM）, thermogravimetric analysis（TGA）, differential scanning calorimetry（DSC）, and polarized light microscopy（PLM）. The nanoscaled dispersion of MgAI（DS） nanolayeres in the PP matrix was verified by the disappearance of the d（003） XRD diffraction peak of MgAI（DS） and observation of TEM image. The DSC data show that the SDS/LDH inorganic components negatively affect the crystallization properties of PP and decrease the size of PP sphcrulites because the inorganic components act as additional nuclei. The PP/MgA1 LDH nanocomposites have a faster charring progress in a temperature range of 250--430 ℃ and a better thermal stability above 320℃ than pure PP.