Polypropylene Clay Research Articles

THE EFFECTS OF OPFB SIZE ON THE MECHANICAL PROPERTIES OF OIL PALM FRUIT BUNCH FIBRE FILLED POLYPROPYLENE–CLAY NANOCOMPOSITES

Oil palm fruit bunch (OPFB) fibre was used as filler in polypropylene–clay nanocomposite (PNC) to study its effect on the mechanical properties of OPFB filled PNC or hybrid polymer nanocomposite (HPNC). The OPFB size was varied at 250 μm, 180 μm, 125 μm and 100 μm. HPNC was prepared by compounding 20 wt.% of OPFB together with PNC. Tensile, flexural and impact test samples were injection moulded from the compounds according to ASTM standards. The experimental results showed that the increase of OPFB size in HPNC has increased the tensile and flexural moduli from 39% to 54% and 33% to 69%, respectively. Meanwhile, the tensile and flexural strengths increased as the OPFB size increases. The elongation at break and impact resistance were not affected by OPFB size. Scanning electron microscope result showed that the fracture surfaces of coarser OPFB filled polypropylene–clay nanocomposite has several mechanisms such as fibre pull-outs, fibre fracture and fibre delamination, whereas the PNC filled with finer OPFB exhibited ductile fracture.

A spectroscopic approach for structural characterization of polypropylene/clay nanocomposite

This study focuses on the degree of dispersion and structural development of organomodified MMT clay (OMMT) during processing of polypropylene clay nanocomposites using both conventional and nonconventional characterization techniques. PP-g-MA and Cloisite 15A were melt blended with three different grades of PP separately in a micro-twin screw compounder at selected screw speed and temperature. The clay was modified with fluorescent dyes and the adsorbed dye content in the clay gallery was estimated by using UV-spectrophotometric method. The effects of residence time and molecular weight of the PP matrix on the clay dispersion were studied. The extent of dispersion and exfoliation of the clay in polymer matrix determined from the torque versus time data obtained from microcompounder. It was further supported by XRD, SEM, TEM, and DSC analysis. Offline dielectric and fluorescence spectrophotometric studies were also carried out. Changes in dielectric constant and dielectric loss with both frequency and temperature yielded quantitative information about the extent of clay exfoliation and intercalation in the polymer matrix. It was observed that with an increase in MFI (decrease in molecular weight) and mixing time, the extent of clay dispersion and exfoliation were also improved due to easy diffusion of polymer chains inside clay gallery. POLYM. COMPOS., 31:2007–2016, 2010. © 2010 Society of Plastics Engineers

STABILITAS TERMAL GALERI CLAY PADA KOMPOSIT NANO POLIPROPILENA-CLAY MONTMORILLONIT DENGAN PENGKOMPATIBEL POLIPROPILENA-g-MALEIK ANHIDIRIDA

Thermal Stability of Clay's Galleries in Polypropylene - Clay (montmorillonite) Nanocomposites using Polypropylene-gMaleic Anhydride as Compatibilizer. Superior properties of food packaging can be achieved using nanocomposite technology. However, fabrication of this materials are complex and expensive. Long term objectives of this research is the synthesis of low cost polypropylene clay nanocomposites (PPCN) via a short-cut method known as ‘cascade engineering’. Cascade engineering principle in PPCN fabrication is performed by using compatibilizer (to enable the mixing of PP and clay) masterbatch, and PPCN in one pot process using melt mixer. This paper present the experimental results using small-angle x-ray diffraction (XRD) on the thermal stability of the PPCN. Results from the XRD analysis showed that the clay was intercalated, however no significant changes were observed as a result of variation in mixing time. XRD patterns of the annealed PPCN showed reduction of MMT’s gallery (deintercalation) These phenomenon was probably caused by insufficient bonding and lack of compatibility between PP-g-MA and MMT.

A new model for estimation of the thermal conductivity of polymer/clay nanocomposites

AbstractHigh density polyethylene– and polypropylene–clay nanocomposites are synthesized by melt blending, in which polyethylene glycol and polypropylene glycol are used as compatibilizers to increase the space of galleries. The morphology properties of nanocomposites are explored by X‐ray diffraction and transition electron microscopy. The thermal conductivity coefficient (K) of nanocomposites is also measured along with the thermal stability. A conventional model based on developed Maxwell‐Garnett formula is also established to predict the thermal conductivity of polymer/clay nanocomposites with clay loading. Morphology results indicate that two intercalated and exfoliated structures are formed. The established model satisfactorily predicts the K values of nanocomposites for low range of clay content. Thermogravimetric analysis shows remarkable thermal stability of nanocomposites with 10 wt % of clay content. The deviation of our model from experimental result for 10 wt % of clay can be attributed to the intercalated structure of layered silicates into the matrices. Although the K values do not considerably increase in 5 wt % with respect to the increase occurs for 10 wt % of clay, but it increases about 28 and 37% at 50°C for high density polyethylene– and polypropylene–clay nanocomposites, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Structure–property relationships in biaxially deformed polypropylene nanocomposites

Semi-solid forming processes such as thermoforming and injection blow moulding are used to make much of today’s packaging. As for most packaging there is a drive to reduce product weight and improve properties such as barrier performance. Polymer nanocomposites offer the possibility of increased modulus (and hence potential product light weighting) as well as improved barrier properties and are the subject of much research attention. In this particular study, polypropylene–clay nanocomposite sheets produced via biaxial deformation are investigated and the structure of the nanocomposites is quantitatively determined in order to gain a better understanding of the influence of the composite structure on mechanical properties. Compression moulded sheets of polypropylene and polypropylene/Cloisite 15A nanocomposite (5 wt.%) were biaxially stretched to different stretching ratios, and then the structure of the nanocomposite was examined using XRD and TEM techniques. Different stretching ratios produced different degrees of exfoliation and orientation of the clay tactoids. The sheet properties were then investigated using DSC, DMTA, and tensile tests .It was found that regardless of the degree of exfoliation or orientation, the addition of clay has no effect on percentage crystallinity or melting temperature, but it has an effect on the crystallization temperature and on the crystal size distribution. DMTA and tensile tests show that both the degree of exfoliation and the degree of orientation positively correlate with the dynamic mechanical properties and the tensile properties of the sheet.

Overall crystallization behavior of polypropylene–clay nanocomposites; Effect of clay content and polymer/clay compatibility on the bulk crystallization and spherulitic growth

AbstractThe effect of clay nanoparticles on the overall crystallization (isothermal crystallization, spherulitic growth, and nonisothermal crystallization) behavior of polypropylene (PP) was studied by means of differential scanning calorimetry and polarized light optical microscopy. In addition, the changes produced by the compatibility between the filler and the matrix were analyzed by using more hydrophobic clays or incorporating PP grafted with maleic anhydride (PP‐g‐MA). Different models were used to predict the relative degree of crystallinity and several parameters were analyzed. A clear nucleating effect of clay nanoparticles was found on the experimental behavior (induction time, half‐crystallization time, and overall crystallization time) and also deducted from the models parameters (Avrami exponent, rate constant, nucleation activity, activation energy). The effect was also related with the matrix/clay compatibility. In addition, the polarized light optical microscopy showed that the number of spherulites increased and their size decreased when clay was incorporated, which is also an indication of the heterogeneous nucleating behavior of such particles. We also noted faster spherulitic growth and increasing Kg (the model parameter). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

SAXS Analysis of Polypropylene-Layered Silicate Nanocomposites: An Integrated Correlations Functions Approach Using an Exfoliation Factor

Use of correlation function and interface distribution function to obtain the morphological parameters from Small Angle X-ray Scattering data makes it as an important quantitative method to evaluate lamellar morphology. Analysis using correlation function assumes lamellar stack morphology with variation of electron density along one dimension where lateral width of lamellae is much larger than the long period normal to the lamellae and the electron density varies with a rectangular profile for alternating crystalline and amorphous layers. In this work, a modified Porod law approach is used for the deviation from ideal two phase model and the thickness of transition zone with variation in electron densities is calculated. Morphological parameters of various grades of organically modified Polypropylene clay nanocomposites, such as long period, linear crystallinity, lamellar thickness and amorphous thickness are estimated using a combination of correlation and interface distribution function. Presence of transition zones does not influence the values for amorphous layer thickness, crystalline layer thickness and long period. Variations in values of long period calculated from correlation and interface function suggest a distribution of lamellar sizes in the polymer and nanocomposites. A new model consisting of the integrated correlation function of polymer and organoclay was developed to quantify the extent of exfoliation of organoclay in the nanocomposites by introducing a parameter, the exfoliation factor, beta. For a highly non-exfoliated system, the large number of clay tactoids is highly correlated and interacting, the correlation function of nanocomposites will be similar to that of nanoclay samples with low values of exfoliation factor. The correlation function of well exfoliated nanocomposites is similar to neat polymer, and such systems have high values of the exfoliation factor. Moreover, the exfoliation factor, which is easily determined by a scattering experiment, correlated well to the important engineering properties of the nanocomposites.

Isotactic polypropylene modified with clay and hydrocarbon resin: Compatibility, structure and morphology in dependence on crystallization conditions

The influence of a based montmorillonite (MMT) clay on the phase structure, structure, morphology and crystallization behaviour of iPP is investigated. A low molecular mass hydrocarbon resin, containing hydroxyl and acid groups, suitable to interactions probably through hydrogen bonding with the polar surface of the clay, was also added to iPP/clay system with the aim to increase the compatibility between iPP and clay and then to improve the performance of such nanocomposites. The crystallization conditions as well as the blend formulation dictate the phase structure, the clay interlayer distances and the iPP polymorphism. In the ternary system intercalation and probably exfoliation of clay layers can be obtained in dependence on thermal treatments. These results open new perspectives to the preparation of homogeneous polypropylene clay nanocomposites and can be the base for further investigation aiming at optimizing the nanomaterials processing conditions.

Biaxial deformation behavior and mechanical properties of a polypropylene/clay nanocomposite

Polymer nanocomposites offer the potential of enhanced properties such as increased modulus and barrier properties to the end user. Much work has been carried out on the effects of extrusion conditions on melt processed nanocomposites but very little research has been conducted on the use of polymer nanocomposites in semi-solid forming processes such as thermoforming and injection blow molding. These processes are used to make much of today’s packaging, and any improvements in performance such as possible lightweighting due to increased modulus would bring significant benefits both economically and environmentally. The work described here looks at the biaxial deformation of polypropylene–clay nanocomposites under industrial forming conditions in order to determine if the presence of clay affects processability, structure and mechanical properties of the stretched material. Melt compounded polypropylene/clay composites in sheet form were biaxially stretched at a variety of processing conditions to examine the effect of high temperature, high strain and high strain rate processing on sheet structure and properties. A biaxial test rig was used to carry out the testing which imposed conditions on the sheet that are representative of those applied in injection blow molding and thermoforming. Results show that the presence of clay increases the yield stress relative to the unfilled material at typical processing temperatures and that the sensitivity of the yield stress to temperature is greater for the filled material. The stretching process is found to have a significant effect on the delamination and alignment of clay particles (as observed by TEM) and on yield stress and elongation at break of the stretched sheet.

Preparation of polypropylene–clay nanocomposites by the co‐intercalation of modified polypropylene and short‐chain amide molecules

AbstractThe effect of short‐chain amide (AM) molecules on the intercalation of montmorillonite clay has been investigated by the melt blending of polypropylene (PP) with clay in the presence of AM molecules such as 13‐cis‐docosenamide (erucamide). Polypropylene–clay nanocomposites (PPCNs) were prepared by the co‐intercalation of maleic anhydride grafted polypropylene (PP–MA) and an AM compound. The resulting nanocomposite structures were characterized with X‐ray diffraction (XRD) and transmission electron microscopy, whereas the thermal characterization of the PPCNs was conducted by thermogravimetric analysis. XRD results showed that the AM molecules intercalated into clay galleries and increased the interlayer spacing, a result confirmed by surface energy (contact angle) and melt flow index measurements. This additive allowed the formation of an intercalated nanocomposite structure, but an exfoliated PPCN structure was also formed with the use of AM with a PP–MA‐based compatibilizer. A new preparation method for PPCNs was, therefore, developed by the co‐intercalation of AM and PP–MA; this resulted in a significantly improved degree of intercalation and dispersion. The enhanced thermal stability of PPCN, relative to pure PP, further demonstrated the improved clay dispersion in the nanocomposite structures prepared by this method. A possible mechanism for the co‐intercalation of AM and PP–MA into the clay galleries is proposed, based on hydrogen bonding between these additives and the silicate layers. Consideration is also given to possible chemical reactions and physical interactions in this rather complex system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Quantification of organoclay dispersion and lamellar morphology in poly(propylene)–clay nanocomposites with small angle X-ray scattering

Intensity profiles of small angle X-ray scattering (SAXS) curves were analyzed to simultaneously gain quantitative information on nanoclay dispersion as well as lamellar ordering in polypropylene–clay nanocomposites. Different types of PP nanocomposites prepared with PP homopolymer (HPP), random propylene–ethylene copolymer (RCP) and a high impact polypropylene–ethylene propylene rubber (ICP) were analyzed. Various one-dimensional models for stacked structures were applied on Lorentz corrected SAXS spectra to derive long period, thicknesses of alternating high and low electron density layers and their distributions, and the number of stacks for both nanoclay and PP lamellae. We applied a mixed thickness distribution model comprising combined Gaussian and exponential for a simple stack of finite thickness, which was found to explain the experimental data better for both nanoclay tactoids and lamellar stacks, compared to simple Gaussian and exponential thickness distributions. Long period X and number of stacks N were derived as important parameters signifying changes in levels of nanoclay exfoliation in PP. Among the three types of polypropylenes studied, better nanoclay exfoliation was obtained for the high impact ICP grade compared to HPP and RCP. Complete exfoliation of nanoclay was achieved in ICP matrix, employing a masterbatch processing route. Moreover, role of nanoclay as a γ nucleating agent was evident from small and wide angle X-ray analyses, and was seen strongly in RCP. Changes in lamellar structure of PP as a result of nanoclay incorporation, double population consisting of both α and γ polytypes in the nanocomposites from that of a primarily α population in neat polymer matrices, were also analyzed in detail with the mixed thickness distribution model, thereby demonstrating its usefulness.

Effect of nanoclays on the dyeability of polypropylene nanocomposite fibres

Polypropylene clay fibres loaded with different alkylammonium‐modified montmorillonite were prepared using a melt spinning technique and relationships between the structure and properties of the nanopolypropylene fibres are discussed. Experiments carried out using transmission electron microscopy showed that the chemical structure of the organic modifier and the interlayer spacing of the clay induced different dispersions of the clay, thus improving accessibility of the nano fibre. It is known that nanoclays are effective and efficient sorbents for dyes. Therefore, the dyeing behaviour of the nano polypropylene fibres with two distinct acid dyes and a disperse dye was studied and the build‐up of dyes, measured as colour yield, reported. The best results were obtained when the clay was well dispersed in nanopolypropylene fibres; that is, when maleated polypropylene was added as a compatibiliser and when disperse dye was used. Good wash fastness was then obtained.

Effects of polypropylene-g-(maleic anhydride/styrene) compatibilizer on mechanical and rheological properties of polypropylene/clay nanocomposites

To enhance the dispersibility of clay in polypropylene (PP) matrix, PP-g-(maleic anhydride/styrene) (MA/ST) was prepared as a compatibilizer by graft copolymerization of maleic anhydride (MA) and styrene (ST) with PP. The addition of ST was known to be effective in improving the graft degree. PP/clay nanocomposites with the compatibilizer were prepared by melt intercalation. The X-ray diffraction (XRD) peaks of (0 0 1) plane of the organo-modified montmorillonite (O-MMT) were shifted to lower angles by an addition of PP-g-(MA/ST), indicating the intercalation capability of PP-g-(MA/ST) in the silicate layers. Transmission electron microscopy (TEM) photographs showed that the O-MMT in the presence of PP-g-(MA/ST) was intercalated and partly exfoliated during melt mixing. The addition of O-MMT and PP-g-(MA/ST) improved the thermal stability, tensile and rheological properties of the nanocomposites.

Polypropylene–clay nanocomposite structure probed by H NMR relaxometry

In this paper, we used low-field nuclear magnetic resonance (NMR) relaxometry and X-ray diffraction techniques to characterize polypropylene and to probe the polypropylene/clay interactions in non-exfoliated and exfoliated polypropylene–clay nanocomposites. Differences in T 1 H longitudinal relaxation time data and X-ray diffraction spectra were correlated with the presence of different domains in the samples studied. The results demonstrated the potential of H NMR relaxometry as a tool in the characterization of polymer–clay nanocomposites.

Polypropylene fibers containing dispersed clays having improved fire performance. I. Effect of nanoclays on processing parameters and fiber properties

AbstractWhile the present interest in the use of functionalized nanoclays as additives for improving tensile properties and fire performance in polypropylene thermoplastics has led to a considerable literature, little attention has been given to this polymer in fiber form. In this article, we report the conditions necessary for and the characteristics of filaments and tapes comprising dispersions of functionalized clay in polypropylene–clay prepared by melt compounding polypropylene in a twin screw extruder. A small fraction (1–3% w/w) of modified grafted polypropylene has also been included to improve dispersion of the clay. X‐ray diffraction of hot‐pressed films, coupled with transmission electron microscopic investigation has been used to assess the degree of dispersion of the clay. Clay dispersion at the nanolevel was observed by TEM, but intercalation was not evident from X‐ray study. Compounded samples were melt‐extruded into filaments using a single screw extruder and drawn prior to wind up. The physical properties of the clay‐containing polypropylene filaments showed that presence of dispersed clay increased filament modulus and was supportive of having achieved some degree of nanodispersion. Selected filament samples had sufficiently acceptable textile properties to enable their knitting into fabric samples. The burning behavior of fabric and film samples were observed by limiting oxygen index and cone calorimetry at 35 kW/m2 external heat flux. While the clay presence did not confer flame retardancy, it did change the burning character and encouraged some char formation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Ultrasound‐aided extrusion process for preparation of polypropylene–clay nanocomposites

AbstractTwo methods for the fabrication of polypropylene/clay nanocomposites using a continuous ultrasound assisted process are compared. In the first approach, a two‐stage process was implemented. The nanocomposites were prepared by using a corotating twin‐screw extruder followed by a single‐screw extruder equipped with an ultrasonic die attachment. In the second method, a single‐stage process was used. The nanocomposites were compounded by using a single‐screw extruder with mixing elements and an ultrasonic die attachment. Two regimens of feeding were realized, namely, starved and flood feeding. The gap size in the ultrasonic treatment zone was varied. Die pressure and power consumption were measured. Similarities and differences of nanocomposites obtained by these two methods are discussed on the basis of their rheological and mechanical properties and their structural characteristics. J. VINYL ADDIT. TECHNOL., 13:40–45, 2007. © 2007 Society of Plastics Engineers.

On striking variation in impact toughness of polyethylene–clay and polypropylene–clay nanocomposite systems: The effect of clay–polymer interaction

The reinforcement of polyethylene and polypropylene with 4 wt.% nanoclay exhibits a striking variation in impact toughness behavior in the temperature range of −40 to +70 °C under identical processing conditions. The reinforcement of polypropylene with nanoclay increases the impact strength, while polyethylene experiences a decrease in the impact strength. To explain this dissimilar and contrasting behavior, we discuss here the possibility of clay–polymer interaction based on conclusions derived from differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), transmission electron microscopy (TEM), wide-angle X-ray diffraction (WAXD), and Fourier transform infrared spectroscopy (FTIR). The observations suggest the possibility of a strong polypropylene–clay interaction, whereas the polyethylene–clay interaction is weak. The strong interaction in polypropylene–clay system is responsible for significant change in physical and mechanical properties.

Ubiquity of soft glassy dynamics in polypropylene–clay nanocomposites

The rheology of polypropylene–clay nanocomposites was studied as a function of organoclay loading, degree of exfoliation, and presence of maleic anhydride functionalized polypropylene compatibilizer. Samples exhibit varying degrees of solid-like response in the terminal regime of small-amplitude oscillatory shear (SAOS), certifying that differences in clay silicate delamination were achieved for fixed organoclay loading. Previous work has also demonstrated that mechanically percolated nanocomposites exhibit logarithmically increasing storage modulus with time at low frequency, behavior attributed to the continuous development of a mesoscale organoclay network akin to that observed for colloidal gels. Continuous low frequency SAOS experiments not only affirm such behavior but also reveal that it is ubiquitous to polypropylene–clay nanocomposites, including samples whose organoclay loading and extent of exfoliation place them below the ostensible mechanical percolation threshold. Similar experiments conducted on uncompatibilized samples support the analogy to soft glassy dynamics, whereby van der Waals attractions drive the formation of a heterogeneous, gel-like organoclay network. Intermolecular associations between pendant group functionalities on the compatibilizer have contributed to logarithmic increases in the storage modulus with time for pure maleated samples, but the reduced concentrations of maleated polypropylene present in the materials reported here are shown to not influence the solid-like rheology over time through network formation. Thus, we demonstrate that only organoclay network formation is responsible for the time-dependent rheology in polyolefin nanocomposites.

Processing of polypropylene–clay nanocomposites: Single‐screw extrusion with in‐line supercritical carbon dioxide feed versus twin‐screw extrusion

AbstractThis work investigates two different melt‐blending strategies for preparing compatibilized polypropylene‐clay nanocomposites, specifically: (1) conventional twin‐screw extrusion, and (2) single‐screw extrusion capable of direct supercritical carbon dioxide (scCO2) feed to the extruder barrel. Proportional amounts (3 : 1) of maleic anhydride functionalized polypropylene compatibilizer and organically modified montmorillonite clay at clay loadings of 1, 3, and 5 wt % are melt‐blended with a polypropylene homopolymer using the two approaches. The basal spacing, degree of exfoliation, and dispersion of organoclay is assessed using X‐ray diffraction, transmission electron microscopy, and rheology. In terms of the latter, both steady shear and small‐amplitude oscillatory shear provide information about the apparent yield stress and solid‐like terminal behavior respectively. Finally, nanoindentation is performed to determine the room temperature modulus of each melt‐blended nanocomposite. The results reveal unequivocally that the high shear of the twin‐screw process is vastly superior to the single‐screw with in‐line scCO2 addition in generating well‐exfoliated, percolated polypropylene‐clay nanocomposites. It is likely that increased contact time between clay and scCO2 is necessary for scCO2 to positively affect exfoliation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 884–892, 2007

Polypropylene–clay nanocomposites: Influence of low molecular weight polar additives on intercalation and exfoliation behavior

AbstractThe influence of low molecular weight additives containing polar groups and modified polyolefin‐based compatibilizers on polypropylene (PP)‐clay nanocomposites (PPCN) has been studied, in terms of intercalation and degree of exfoliation achievable by melt‐state mixing processes. PPCN were prepared by melt mixing two PP homopolymers with organically‐modified montmorillonite type clay, in the presence of maleic anhydride‐grafted polypropylene (PP‐MA) compatibilizer. XRD analysis shows that interlayer spacing of clay has been increased dramatically, while TEM results show a significant improvement of clay dispersion in the PP matrix, when nanocomposites are prepared with commercial PP containing short‐chain organic additives with polar end groups. Subsequent studies based upon customized PP formulations, with amide‐type slip additive, confirm the intercalation of this additive into the clay galleries and its positive and significant impact on clay dispersion. Contact angle measurements suggest that these additives diffuse into the clay gallery space rather than migrating away from the bulk of the PPCN matrix. The interaction between polar group (NH2) of this additive and the polar sites on the filler surface appears to be the driving force for the intercalation. POLYM. ENG. SCI. 46:1008–1015, 2006. © 2006 Society of Plastics Engineers