Effect of the ratio of maleated polypropylene to organoclay on the structure and properties of TPO-based nanocomposites. Part II: Thermal expansion behavior

Significant reductions in linear thermal expansion coefficients in the flow and transverse directions of injection-molded specimens of thermoplastic polyolefin, or TPO, nanocomposites were achieved by controlling the maleated polypropylene (PP-g-MA)/organoclay ratio. Linear thermal expansion behavior was examined using a thermomechanical analyzer (TMA). The trends in thermal expansion for the nanocomposites are discussed in terms of the morphology of both dispersed clay and elastomer phases by means of transmission electron microscopic (TEM) and atomic force microscopic (AFM) observations and subsequent particle analyses. A higher PP-g-MA/organoclay ratio causes an increase in the aspect ratio of clay particles along the flow direction (FD) and transverse direction (TD) for the injection-molded specimens; however, the aspect ratio along the FD was higher than that along the TD. On the other hand, the aspect ratio of elastomer particles along the FD was much higher than that along the TD. Furthermore, highly elongated elastomer particles along the FD were observed. The combined effect of the mechanical constraint by organoclay and the highly elongated elastomer particles caused at high PP-g-MA contents was responsible for the significant reduction of thermal expansion for these materials.     

TPO based nanocomposites. Part 1. Morphology and mechanical properties

The relationship between morphology and the mechanical properties of thermoplastic olefin (TPO) materials that are reinforced with organoclay fillers and prepared by melt processing is reported. Nanocomposites based on blends of polypropylene and elastomer and using an organoclay masterbatch were prepared in a twin-screw extruder. Transmission electron microscopy, atomic force microscopy and wide-angle X-ray scattering were employed to carry out a detailed particle analysis of the morphology of the dispersed clay and elastomer phases for these nanocomposites. The improvement in mechanical properties, e.g. stiffness enhancement as evaluated by stress-strain analysis and impact strength obtained from notched Izod impact tests, were successfully explained in terms of morphological changes induced by the presence of the clay and elastomer particles. Quantitative analyses of TEM micrographs and AFM images revealed a decrease in the aspect ratio of the clay particles and a reduction in the size of elastomer particles with increasing clay content. In addition, WAXD scans indicated a skin-core effect for the injection molded specimens in terms of both polypropylene crystal orientation and clay filler orientation. This information is essential for the understanding of the mechanism of mechanical property enhancement in nanocomposite materials.     

The effect of clay type and of clay–masterbatch product in the preparation of polypropylene/clay nanocomposites

Clay containing polypropylene (PP) nanocomposites were prepared by direct melt mixing in a twin screw extruder using different types of organo‐modified montmorillonite (Cloisite 15 and Cloisite 20) and two masterbatch products, one based on pre‐exfoliated clays (Nanofil SE 3000) and another one based on clay–polyolefin resin (Nanomax‐PP). Maleic anhydride‐grafted polypropylene (PP‐g‐MA) was used as a coupling agent to improve the dispersability of organo‐modified clays. The effect of clay type and clay–masterbatch product on the clay exfoliation and nanocomposite properties was investigated. The effect of PP‐g‐MA concentration was also considered. Composite morphologies were characterized by X‐ray diffraction (XRD), field emission gun scanning electron microscopy (FEG‐SEM), and transmission electron microscopy (TEM). The degree of dispersion of organo‐modified clay increased with the PP‐g‐MA content. The thermal and mechanical properties were not affected by organo‐modified clay type, although the masterbatch products did have a significant influence on thermal and mechanical properties of nanocomposites. Intercalation/exfoliation was not achieved in the Nanofil SE 3000 composite. This masterbatch product has intercalants, whose initial decomposition temperature is lower than the processing temperature (T ～ 180°C), indicating that their stability decreased during the process. The Nanomax‐PP composite showed higher thermal and flexural properties than pure PP. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Modeling the mechanical and thermal expansion behavior of TPO-based nanocomposites

The modulus and coefficient of thermal expansion (CTE) of polypropylene-based nanocomposites and blends were predicted using various composite theories and compared to experimental results. The Mori-Tanaka and Chow model predictions best match the previously reported experimental trends, though the Chow model underestimates the CTE in the normal direction (ND). Of the various ternary-phase approaches used to predict the modulus and CTE of thermoplastic polyolefin (TPO) nanocomposites, a multiplicative approach wherein the contribution of the clay is calculated first and the nanocomposite is then considered to be the matrix for the elastomer blend best matches the experimental trends. The models better capture the effects of the MMT than those of the ethylene-octene elastomer, EOR. A different model predicting the effect of the MMT tactoids on the experimental TPO gives rather good quantitative agreement between the predicted and experimental values of modulus and CTE for TPO nanocomposites.     

Microstructure‐properties correlations in dynamically vulcanized nanocomposite thermoplastic elastomers based on PP/EPDM

Thermoplastic vulcanized (TPV) nanocomposites were prepared in a laboratory mixer using EPDM, polypropylene of different viscosities, maleic anhydride modified polypropylene, an organo‐clay, and a sulfur‐based curing system. Based on the obtained results from X‐ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential scanning calorimeter, and mechanical properties, the microstructure of the prepared nanocomposites was found to be sensitive to the viscosity difference between the two phases and the clay content. X‐ray diffraction and TEM images of the TPV nanocomposites showed that clay was nearly exfoliated and randomly distributed into the polypropylene phase. The SEM photomicrographs of the dynamically vulcanized thermoplastic elastomer samples showed that the rubber particles were dispersed through the polypropylene in form of aggregates and their size increased with the introduction of clay. The nanoscale dimensions of the dispersed clay resulted in a significant improvement of the tensile modulus of the TPV nanocomposite samples, from 20 to 90% depending on clay content and the viscosity ratio of PP/EPDM. In the PP nanocomposites, the clay layers act as nucleating agents, resulting in higher crystallization temperature and reduced degree of crystallinity. Moreover, the oxygen permeability in the TPV nanocomposites was found to be lower than in unfilled but otherwise similar materials. POLYM. ENG. SCI., 47:207–217, 2007. © 2007 Society of Plastics Engineers.     

Chlorosulfonated polypropylene: preparation and its application as a coupling agent in polypropylene-clay nanocomposites

Polypropylene nanocomposites containing organophilic layered silicate were prepared by melt mixing. In order to increase polypropylene polarity, Cl and SO₂Cl groups were introduced by reaction with sulfuryl chloride under UV irradiation. Chlorosulfonated polypropylene was subsequently melt-compounded with organophilized montmorillonite clay to produce a masterbatch. The masterbatch was then blended with commercial isotactic polypropylene. An organophilized silicate (Cloisite 15A) and three chlorosulfonated polypropylenes with different degrees of functionalization were used in this study. The effect of various processing procedures was examined as well. The morphology of nanocomposites obtained was examined using TEM and X-ray diffraction. It has been shown that the presence of polar groups leads to an increased gallery distance and partial exfoliation. Nevertheless, full exfoliation of clay platelets has not been achieved. The observed morphologies affected the resulting tensile mechanical behaviour: both stiffness and strength significantly increased.     

Dispersion and flame retardancy of ethylene vinylacetate/layered silicate nanocomposites using the masterbatch approach for cable insulating material

Ethylene vinylacetate (EVA) copolymer-based nanocomposites with maleic anhydride-grafted ethylene-vinylacetate (EVAgMA) and organically modified clay (o-clay) were prepared in a twin screw extruder by following a two-step melt compounding method. EVAgMA/o-clay masterbatches with various clay contents up to 50 wt% were examined, after which the masterbatch with the highest clay content was melt compounded with EVA for the preparation of EVA/o-clay nanocomposites containing specific amounts of clay. Further morphological dispersion of the clay particles by highly polar EVA and shearing was confirmed in the EVA/o-clay nanocomposites by X-ray diffraction (XRD) and transmission electron microscopy (TEM). These morphologies led to increased thermal properties in air as well as a considerable decrease in heat release rate (HRR). EVA/o-clay/MDH nanocomposites were also prepared using a high clay-bearing masterbatch to confirm the synergistic flame retardancy of clay as a co-additive in EVA/MDH composites. EVA/o-clay/MDH nanocomposites prepared by substituting o-clay for MDH showed significantly lower and wider HRR during combustion compared to EVA/MDH composite.     

Anisotropic thermal expansion in polypropylene/poly(ethylene-co-octene) binary blends: influence of arrays of elastomer domains

In injection molded specimens consisting of isotactic polypropylene (iPP)/poly(ethylene-co-octene) (EOR) blends with different viscosity ratio of η(EOR)/η(iPP), the coefficient of linear thermal expansion (CLTE) was investigated by thermal mechanical analysis (TMA). It was found that the blend with a smaller viscosity ratio showed the larger anisotropy of CLTE depending upon the directions. TEM observations revealed that the shape of rubber domains varied from slabs, cylinders to ellipsoids in shape, by increasing η(EOR)/η(iPP). The crystal orientation analysis by WAXD have revealed that the blend with ‘slab’ EOR domains showed the orientation of the c-axis of iPP crystals was preferably oriented to FD (flow direction) and TD (transverse to FD), and that the b-axis was exclusively oriented to ND (thickness direction). The CLTE of each FD and TD was in good agreement with the rules-of-mixing for CLTE by introducing the effect of the arrays of the elastomer domains and the PP crystal orientation. On the other hand, the CLTE in ND showed massive discrepancy between the calculation and observation. It was found that the incorporation of the retraction effect could explain the discrepancy to some extent.     

Interfacially compatibilized LDPE/POE blends reinforced with nanoclay: investigation of morphology,rheology and dynamic mechanical properties

Morphological, melt rheological and dynamic mechanical properties of low-density polyethylene (LDPE)/ethylene–octene copolymer (POE)/organo-montmorillonite (OMMT) nanocomposites, prepared via melt compounding were studied. The XRD traces indicated different levels of intercalated structures for the nanocomposites. Addition of a compatibilizer (PE-g-MA) improved the intercalation process. TEM results revealed existence of clay layers in both phases but they were mainly localized in the elastomeric POE phase. Addition of 5 wt% OMMT to the LDPE/POE blend led to reduction in the size of the elastomer particles confirmed by AFM. The complex viscosity and storage modulus showed little effect of the presence of the clay when no compatibilizer was added. As the extent of exfoliation increased with addition of compatibilizer, the linear viscoelastic behavior of the composites gradually changed specially at low-frequency regions. The interfacially compatibilized nanocomposites with 5 wt% OMMT had the highest melt viscosity and modulus among all the studied nanocomposites and blends. Also, this particular composition showed the best improvement in dynamic storage modulus. The results indicated that clay dispersion and interfacial adhesion, and consequently different properties of LDPE/POE/clay nanocomposites, are greatly affected by addition of compatibilizer.     

Effect of HfC nanowires grown on carbon fibers on the microstructure and thermophysical properties of C/C composites

One-dimensional (1D) hafnium carbide nanowires (HfCnws) were grown in situ on carbon fibers (CFs) via a Ni-assisted pyrolysis method of organometallic polymer precursor. Scanning electron microscopy (SEM), transmission electron microscope (TEM), polarized-light optical microscopy (PLM), and Raman were used to analyze the effect of HfCnws on the microstructure of pyrolytic carbon (PyC). The specific heat capacity (HC), thermal diffusivity (TD), thermal conductivity (TC), and coefficient of thermal expansion (CTE) of HfCnws-C/C composites were also investigated. Results show that HfCnws wrapped by carbon nanosheet were successfully synthesized. The diameter of HfCnws is about 30 nm and the thickness of carbon nanosheet is about 10 nm, which could induce the formation of isotropic (ISO) PyC. After introducing HfCnws, the TD and CTE of HfCnws-C/C composites were increased. Ni2HfCnws-C/C composites show a higher TC and TD, and the CTE increased with the increasing content of HfCnws.     

Polypropylene-organoclay nanocomposites containing nucleating agents

Polypropylene/organoclay nanocomposites containing nucleating agents, viz., aluminum hydroxybis[2,2-methylenebis(4,6-di-tert-butylphenyl) phosphate (NA21) and 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (Millad 3988), were prepared by direct melt intercalation in a twin-screw extruder. Nucleating agents were added to polypropylene during compounding and their effect on the properties of the nanocomposites was studied. X-ray diffraction (XRD) and transmission electron microscopy (TEM) exhibited clay layers to be intercalated and partially exfoliated. The expansion of inter-gallery distance of the clay layers was governed by the interaction between polypropylene, compatibilizer, and different nucleating agents. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) indicated higher thermal stability and crystallization temperature for nanocomposites compared to virgin polymer. Even a small addition of the nanoscale filler with 0.2% nucleating agents was found to promote concurrently several PP material properties, including improved tensile characteristics, higher Young’s modulus, increased thermal stability and rate of crystallization.     

Enhancement of the thermal stability,mechanical properties and morphologies of recycled PVC/clay nanocomposites

Summary Recycled PVC/clay nanocomposites were prepared by melt mixing of recycled PVCs and modified clays. Characterization of the nanostructure of the nanocomposites was carried out using wide angle X-ray diffraction (WAXD) and transmission electron microscopy(TEM). In case of 10wt.%, the characteristic peak of modified clay was perfectly disappeared, because of aids of plasticizers as co-intercalator. Thermal stability was evaluated from the thermal decomposition behaviors and linear dimension changes by TGA and TMA system. Coefficients of thermal expansion of the nanocomposites were also observed from TMA analysis. Dynamic mechanical properties were evaluated using DMA system. The thermal and mechanical properties of the nanocomposites were improved simultaneously for varied clay loadings, 1,3,5,10wt.%, compared to recycled PVC. Especially, the storage modulus of the nanocomposites with 10wt.% clay loading was increased 11 times compared to that of recycled PVC.     

Synergistic effect of organo‐montmorillonite on intumescent flame retardant ethylene‐octene copolymer

Nanocomposite of thermoplastic elastomer ethylene‐octene copolymer/maleated ethylene‐octene (POE/POE‐g‐MAH) with organo‐montmorillonite (OMMT, 11 wt %) as masterbatch have been obtained by melt blending and it has been characterized by transmission electron microscopy (TEM). Flame retardant POE/POE‐g‐MAH/OMMT/ammonium polyphosphate‐pentaerythritol (APP‐PER) (an intumescent flame retardant with 75 wt % ammonium polyphosphate and 25 wt % pentaerythritol) composites were prepared by using melting processing to study their structures, flame‐retardancy, thermal, and mechanical properties. TEM showed exfoliated structures throughout POE/POE‐g‐MAH/OMMT masterbatch and POE/POE‐g‐MAH/OMMT/APP‐PER nanocomposites. Synergistic effect was observed between OMMT and APP‐PER resulting in significant improvements on thermal stability, flame‐retardancy and mechanical properties in the POE/POE‐g‐MAH/OMMT/APP‐PER nanocomposites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of the ratio of maleated polypropylene to organoclay on the structure and properties of TPO-based nanocomposites. Part I: Morphology and mechanical properties

The structure-property relationships of thermoplastic olefin (TPO)-based nanocomposites prepared by melt processing are reported with a main focus on the ratio of maleic anhydride-grafted polypropylene (PP-g-MA) to organoclay. The morphological observations by transmission electron microscopy, atomic force microscopy, and X-ray diffraction are presented in conjunction with the mechanical and rheological properties of these nanocomposites. Detailed quantitative analyses of the dispersed clay particles revealed that the aspect ratio of clay particles decreased as clay content increased but increased as the amount of PP-g-MA increased. Analysis of the elastomer phase revealed that the aspect ratio of the elastomer phase increased in both cases. The presence of clay causes the elastomer particles to become highly elongated in shape and retards the coalescence of the elastomer particles. The modulus and yield strength are enhanced by increasing the PP-g-MA/organoclay ratios. High levels of toughness of the TPO can be maintained when moderate levels of (organoclay) MMT and PP-g-MA are used. The rheological properties suggested that the addition of clay particles and PP-g-MA has a profound influence on the long time stress relaxation of the TPO nanocomposites. Based on these analyses, it is clear that it is important to optimize the ratio of PP-g-MA and organoclay to obtain the desired balance of mechanical properties and processing characteristics for TPO nanocomposites.     

Thermal and Barrier Properties of Organoclay-filled Polysulfone Nanocomposites

Organo-modified fluorohectorite (OFH) clay-filled polysulfone (PSf) nanocomposites were prepared by a solution casting method. The dispersion of OFH clay in PSf nanocomposites was investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). Thermal analysis revealed that incorporation of organoclay increased the thermal stability and glass transition temperature (T_g) of nanocomposites. The barrier properties of the nanocomposites studied were found to be significantly improved. It is worth mentioning that the improved thermal stability and barrier performance of these nanocomposites with the addition of organoclay in PSf matrix obviously offers immense potential in industrial and automobile applications.     

Effects of direct melt compounding and masterbatch dilution on the structure and properties of nanoclay‐filled polyolefins

The differences that direct melt compounding and masterbatch dilution cause in the properties of melt compounded polypropylene (PP) and high density polyethylene‐based (PE‐HD) nanocomposites are presented. The results include comparison of properties and morphology of directly melt processed organoclay nanocomposites with similar compounds diluted from commercial and in‐house‐made masterbatches to clay concentrations of 1, 3, 6, and 8 wt%. The compounds were prepared with a co‐rotating Brabender twin‐screw extruder. The degree of exfoliation and the dispersion of the nanoclay were verified with transmission electron microscopy and X‐ray diffraction. Thermal stability of the materials was examined with thermogravimetric analysis and the mechanical properties of the compounded materials were also determined. The most promising results regarding mechanical behavior were achieved with the in‐house‐made masterbatch in the form of a notable increase in Young's modulus in both matrices. There was also a distinct increase in impact strength when masterbatch was used. Changes were more pronounced in case of PP. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Crystal transformation and thermomechanical properties of poly(vinylidene fluoride)/clay nanocomposites

The crystal transformation and thermomechanical properties of melt‐intercalated poly(vinylidene fluoride) (PVDF)/clay nanocomposites are reported in this study. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to study the thermal properties of PVDF and its nanocomposites with various clay concentrations. The incorporation of clay in PVDF results in the formation of β‐form crystals of PVDF. DSC study of melting behavior suggested the presence of only α‐phase crystals in neat PVDF and both α‐ and β‐phase crystals in the nanocomposite. This conclusion was corroborated by findings from Fourier‐transform infrared (FTIR) spectroscopy and X‐ray diffraction (XRD). Dynamic mechanical analysis (DMA) indicated significant improvements in storage modulus over a temperature range of 20–150 °C. The coefficient of thermal expansion (CTE) decreases with increasing clay loading. Copyright © 2004 Society of Chemical Industry     

Melt processing and characterization of polypropylene/pristine montmorillonite nanocomposite: Influence of compatibilizer and hyperbranched polymer

In the present investigation, nanocomposites of polypropylene (PP)‐montmorillonite (MMT) clay were prepared by a single‐step compounding method to study the influence of hyperbranched polyester (HBPE) on rheological and mechanical properties of PP composites in the presence of a compatibilizer. In service of this objective, polyvinylchloride‐grafted‐maleic anhydride (PP‐g‐MA) was used as a compatibilizer for hydrophobic PP and hydrophilic clay. Rheological property in terms of melt viscosity was examined by a Brabender torque rheometer. The composite's morphology was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), whereas the dispersion state of nanoparticles in the PP matrix was studied by X‐ray diffraction (XRD). The thermal behavior of nanocomposites was examined by differential scanning calorimetry (DSC). The analysis of results confirmed that the interactions among both additives significantly influenced the morphology, rheology, and thermomechanical properties of the nanocomposites. J. VINYL ADDIT. TECHNOL., 22:72–79, 2016. © 2014 Society of Plastics Engineers     

Water-assisted extrusion of polypropylene/clay nanocomposites: A comprehensive study

Water-assisted extrusion process has been used to successfully prepare polypropylene (PP)/clay nanocomposites with high degree of clay delamination and markedly improved rheological, thermal and mechanical properties. PP-graft-maleic anhydride (PP-g-MA)-based nanocomposites and masterbatches were synthesized from untreated clay and organoclay, respectively, and fully characterized. The effects of using high-shear rates and water injection during the melt-compounding were examined. A mechanism explaining the formation of such nanocomposites is then proposed. The best clay dispersion and properties improvements of PP-g-MA/organoclay nanocomposites and masterbatches were obtained using high-shear rates and water injection (synergy effect). PP-based nanocomposites were then synthesized by dilution of PP-g-MA-based masterbatches into neat PP. For comparison, nanocomposites were also prepared by a one-pot process where PP, PP-g-MA and organoclay are directly melt-blended with or without water injection. The nanocomposites prepared by dilution into PP of a masterbatch prepared through water-assisted extrusion showed the highest clay dispersion and consequently the best thermal, mechanical and rheological properties.     

Morphological evolution and mechanical property enhancement of natural rubber/polypropylene blend through compatibilization by nanoclay

Nanocomposites of natural rubber (NR)/polypropylene (PP) (80/20 wt %) blends filled with 5 phr pristine clay were prepared by melt‐mixing process. Effects of clay incorporation technique via conventional melt‐mixing (CV) and masterbatch mixing (MB) methods on nanostructure and properties of the blend nanocomposites were investigated. The XRD, SAXS, WAXD, and TEM results showed that the clays in the NR/PP blend nanocomposites were presented in different states of dispersion and were locally existed at the interface between NR and PP as well as dispersed in the NR matrix. The presence of clay caused unique morphological evolution such as fine fibrillar PP domains. The tensile strength was improved over the unfilled NR/PP blends by 53% and 224%, and the storage modulus at 25 °C was increased by 78% and 120% for the NR/PP/clay nanocomposites prepared by CV and MB methods, respectively. Significant improvement in both properties was particularly obtained from the MB method due to finer dispersion fibrillar PP phase in the NR matrix and stronger interfacial adhesion between NR and PP fibers, as suggested from DMA. The oil resistance of blend nanocomposites was also improved over that of the unfilled NR/PP blend, and this property was further progressed by the masterbatch mixing method. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44574.