Nanostructure and micromechanical properties of reversibly crosslinked isotactic polypropylene/clay composites

Recent developments concerning the methodology used to prepare composites of iPP and nanoclays are reported. Conventional (reactive melt mixing) and in situ preparations were performed, and the structural properties exhibited by the composites are discussed. Results suggest that the nanoclay could exhibit partial and, maybe, total exfoliation within the composites. Adhesion between the polymeric matrix and the nanoclay layers is similar to that obtained after grafting. The experimental procedure used and the analysis performed by means of the wide‐angle X‐ray scattering and differential scanning calorimetry techniques permit to describe, at nanoscale level, the contribution of the nanoclay to the polymer composite system. The microhardness values of the iPP–clay composites depend on the clay content and on the preparation method, and linearly correlate, according to the additivity law, with the degree of crystallinity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of rolling deformation on the structures and properties of multi‐walled carbon nanotube filled isotactic polypropylene

Isotactic polypropylene filled with various contents of multi‐walled carbon nanotubes (MWCNTs) were fabricated by the injection molding technique and then rolled at room temperature. The unrolled samples (URS) and rolled samples (RS) were characterized by X‐ray diffraction studies, scanning electron microscopy, mechanical and micromechanical tests and differential thermal analyses. Although the URS exhibit the lamellar α‐crystal with a*‐axis orientation, the RS show the same crystals with both a*‐ and c‐axis orientation, which is explained by interlamellar and intralamellar slips and lamellar destruction. Scanning electron micrographs display distinct surface morphological features for both URS and RS. While the tensile strength of RS is higher than that of URS, the Young's modulus (Y) is found to be lower than that of URS. Anisotropy in microharness (H) parallel and perpendicular to the rolled direction has been detected, although H for both samples increases with increasing MWCNT contents. The average relationship H/Y ≈ 0.18 as estimated for URS is closer to the predicted value of 0.10 for polymers than the H/Y ≈ 0.22 obtained for RS. The lamellar thickness for URS increases with increase of MWCNT content and that for RS decreases, as evaluated from both differential thermal analyses and X‐ray diffraction data. Copyright © 2011 Society of Chemical Industry     

Influence of regioirregular structural units on the crystallization of isotactic polypropylene

Seven samples of isotactic polypropylene were examined to study the influence on the formation of the γ crystalline phase of possible regiodefects along the chain. Wide‐angle X‐ray diffraction allowed the determination of the percentage of the γ phase in the samples and ¹³C‐NMR spectroscopy was used to correlate the development of the γ phase with the existence of regioirregular structural units along the chain. Furthermore, it was possible to appraise the contributions given by the different families of lamellae to the small‐angle X‐ray diffraction patterns. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 375–384, 2001     

Characterization of latex-based isotactic polypropylene/clay nanocomposites

Polypropylene/clay nanocomposite (PCN) containing 1 wt% organo-modified clay was prepared by latex technology, previously successfully applied for preparation of carbon nanotubes (CNTs)/polymer composites. The level of dispersion of organoclay and the microstructure of the resulting PCNs were characterized by means of X-ray diffraction analysis, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The obtained results have demonstrated that the latex technique represents a promising method for preparation of PP/clay nanocomposites with good dispersion of exfoliated nanoclay particles. The influence of clay nanoparticles on nonisothermal crystallization of PCN was investigated by DSC. The crystallization onset temperature of the matrix rises for about 5 °C when crystallizing from the quiescent melt. Improved thermal stability of PP/nanoclay was observed as evaluated by TGA. The dynamic mechanical analysis reveals an increase in storage modulus of PP matrix in the nanocomposites for 30% over a temperature range, indicating an increase in the stiffness of the material with the addition of organically modified clay.     

Morphology and mechanical properties of polypropylene/organoclay nanocomposites

Polypropylene (PP) nanocomposites were prepared by melt intercalation in an intermeshing corotating twin‐screw extruder. The effect of molecular weight of PP‐MA (maleic anhydride‐ modified polypropylene) on clay dispersion and mechanical properties of nanocomposites was investigated. After injection molding, the tensile properties and impact strength were measured. The best overall mechanical properties were found for composites containing PP‐MA having the highest molecular weight. The basal spacing of clay in the composites was measured by X‐ray diffraction (XRD). Nanoscale morphology of the samples was observed by transmission electron microscopy (TEM). The crystallization kinetics was measured by differential scanning calorimetry (DSC) and optical microscopy at a fixed crystallization temperature. Increasing the clay content in PP‐ MA330k/clay, a well‐dispersed two‐component system, caused the impact strength to decrease while the crystallization kinetics and the spherulite size remained almost the same. On the other hand, PP/PP‐MA330k/clay, an intercalated three‐component system containing some dispersed clay as well as the clay tactoids, showed a much smaller size of spherulites and a slight increase in impact strength with increasing the clay content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1562–1570, 2002     

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.     

Preparation of polyethylene–clay nanocomposites directly from Na+ montmorillonite by a melt intercalation method

Polyethylene (PE)/clay nanocomposites were prepared directly from Na⁺ montmorillonite by a melt intercalation technique, using hexadecyl trimethyl ammonium bromide (C16) as a reactive compatibilizer. Three other polymer–clay nanocomposites were also prepared by this new technique. Their structures were characterized by X‐ray diffraction and transmission electron microscopy. The mechanism of this new method was studied. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2583–2585, 2003     

Tuning the functionalization chemistry of polypropylene for polypropylene/clay nanocomposites

New polypropylene (PP)-graft-maleic anhydride (PP-g-MA) samples have been successfully synthesized by adding N-bromosuccinimide (NBS) during the reactive extrusion process. These NBS-mediated PP-g-MAs possess higher graft content than classic PP-g-MAs (i.e. without NBS) while they keep acceptable molar masses. NBS-mediated PP-g-MAs were used as matrices in model PP-g-MA/organoclay nanocomposites and compared with commercial and home-made classic PP-g-MAs in order to evaluate their ability to disperse the clay. Significantly better degrees of clay delamination and dispersion were reached using NBS-mediated PP-g-MAs than with classic PP-g-MAs. As expected, PP-g-MAs having high graft content showed the best clay dispersion. Within the examined range of molar masses, the PP-g-MA molar mass had no influence on the clay dispersion. However PP-g-MAs exhibiting important reduction of crystallinity lead to poor clay dispersion whatever the graft content. The PP-g-MA/organoclay nanocomposite prepared using the selected “optimized” NBS-mediated PP-g-MA exhibited the best improvement of thermal properties and one of the best clay dispersions. PP/PP-g-MA blends were prepared to evaluate the miscibility between PP and selected PP-g-MAs. No problem of miscibility between the selected NBS-mediated PP-g-MA and PP was noticed. Finally the PP/organoclay prepared using the selected NBS-mediated PP-g-MA as compatibilizer showed much better clay dispersion and thermal stability than the one prepared with the corresponding classic PP-g-MA, thus establishing the interest to use such new NBS-mediated PP-g-MAs as compatibilizers.     

Preparation and physical properties of wood/polypropylene/clay nanocomposites

Wood plastic composites (WPCs) are attracting a lot of interests because they are economic, environmentally friendly, and show fairly good performance. To improve the performance of a wood/polypropylene (PP) composite, an organoclay was incorporated as a nanosize filler in this work. WPCs were prepared by melt blending followed by compression molding, and their performance was investigated by universal testing machine, izod impact tester, dynamic mechanical analyzer, thermal mechanical analyzer, differential scanning calorimetry, and TGA. Maleic anhydride polypropylene copolymer (MAPP) was used to increase compatibility between the PP matrix and wood particles and also improve the dispersion and exfoliation of the organoclay in the PP matrix. XRD analysis showed that the matrix of the WPCs with organoclay had intercalated structure. The SEM images of the WPCs with MAPP showed improved interfacial adhesion between the matrix and wood particles. The degree of water absorption increased with immersion time, but it could be restrained by incorporating MAPP. The performance of the WPCs was improved by the incorporation of the organoclay. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation by melt mixing and characterization of isotactic polypropylene/SiO2 nanocomposites containing untreated and surface‐treated nanoparticles

In the present study two series of isotactic polypropylene (iPP)/SiO₂ nanocomposites containing 1, 2.5, 5, 7.5, and 10 wt % SiO₂ nanoparticles were prepared by melt‐mixing on a twin‐screw corotating extruder. In the first series untreated fumed silica nanoparticles were used, whereas in the second nanoparticles were surface‐treated with dimethyldichlorosilane. In both cases, the average size of the primary nanoparticles was 12 nm. Tensile and impact strength were found to increase and to be affected mainly by the type and content of silica nanoparticles. A maximum was observed, corresponding to samples containing 2.5 wt % SiO₂. These findings are discussed in light of the SEM and TEM observations. By increasing the amount of nanoparticles, large aggregates of fumed silica could be formed, which may explain the reduction of mechanical properties with higher concentrations of SiO₂. However, it was found that surface‐treated nanoparticles produced larger aggregates than did those derived from untreated nanoparticles, despite the increased adhesion of the iPP matrix, as was postulated from yield strength. This behavior negatively affected mechanical properties. In addition, an effort was made to determine if toughening theories, mainly the critical interparticle distance for rubber toughening or composites, also might be applicable in nanocomposites. From DSC measurements it was demonstrated that silica nanoparticles acted as effective nucleating agents, increasing the crystallization rate and the degree of crystallinity of iPP. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2684–2696, 2006     

Further study on double‐melting endotherms of isotactic polypropylene

The origins of the single‐ and double‐melting endotherms of isotactic polypropylene crystallized at different temperatures were studied carefully by differential scanning calorimetry, wide‐angle X‐ray diffraction, and small‐angle X‐ray scattering. The experimental data show that spontaneous crystallization occurs when the crystallization temperature is lower than 117°C; thus the lamellae formed are imperfect. At a lower heating rate, the recrystallization or reorganization of these imperfect lamellae leads to double endotherms. On the other hand, when the crystallization temperature is higher than 136°C, two major kinds of lamellae with different thickness are developed during the isothermal process, which also results in the double‐melting endotherms. In the intermediate temperature range the lamellae formed are perfect, and there is only a single peak in the distribution of lamellar thickness. This explains the origin of the single‐melting endotherm. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 163–170, 2000     

Structural,mechanical and thermal studies of double‐molded isotactic polypropylene nanocomposites with multiwalled carbon nanotubes

Nanocomposites of isotactic polypropylene (iPP) and multiwalled carbon nanotubes (MWCNTs) with various contents of MWCNTs were fabricated by double molding techniques. X‐ray diffraction measurements reveal a development of α‐crystal with lamellar stacks having a long period of 150 Å in the neat iPP that increases to 165 Å in 2 wt % MWCNTs‐loaded composites, indicating that MWCNTs enhance crystallization of iPP as a nucleating factor. Mechanical properties, such as tensile strength, flexural strength, Young's modulus, tangent modulus, and microhardness are found to increase with increasing MWCNTs content. Thermal analyses represent an increase of crystallization and melting temperatures and a decrease of thermal stability of the composites with increasing MWCNTs. Changes in structural, mechanical, and thermal properties of the composites due to the addition of MWCNTs are elaborately discussed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The influence of annealing treatment on the molecular structure and the mechanical properties of isotactic polypropylene fibers

An investigation was carried out on the effects of annealing treatment on the molecular structure and the mechanical properties of isotactic polypropylene fibers annealed in an air heated environment at temperatures ranging from 60 to 140°C. Analysis of the equatorial X‐ray diffraction traces showed the presence of a three phase system of amorphous‐smectic‐monoclinic forms and revealed the transformation of the metastable smectic form to the highly stable monoclinic form as the annealing temperature is increased, resulting in an enhanced degree of crystallinity and the crystallite size. The improvements in the degree of crystallinity and the crystallite size became more remarkable above 120°C. Evaluation of the crystallinity was carried out using an analysis of density, infrared spectroscopy, and X‐ray diffraction methods whereas the state of the molecular orientation was evaluated using polarized infrared spectroscopy measurements only. Polarized infra‐red spectroscopy measurements after the curve fitting procedure showed a slight increase of the molecular orientation of the helical chain segments present in the crystalline phase represented by the IR bands at 841 and 998 cm^?1 whereas the amorphous structure represented by the IR band at 974 cm^?1 showed no significant change with increasing annealing temperature. The improvement in the molecular orientation of the crystalline phase became more remarkable above 120°C. Tensile strength of the annealed fibers increased with increasing annealing temperature but the elongation at break and the initial modulus were not affected as much as the tensile strength. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Structure and melt rheology of long‐chain branching polypropylene/clay nanocomposites

Long‐chain branching polypropylene (LCB‐PP)/clay nanocomposites were prepared by melt blending in a twin‐screw extruder. The microstructure and melt rheology of these nanocomposites were investigated using x‐ray diffraction, transmission electron microscopy, oscillatory shear rheology, and melt elongation testing. The results show that, the clay layers are intercalated by polymer molecular chains and exfoliate well in LCB‐PP matrix in the presence of maleic anhydride grafted PP. Rheological characteristics, such as higher storage modulus at low‐frequency and solid‐like plateau in tan‐ω curve, indicate that a compact and stable filler network structure is formed when clay is loaded at 4 phr (parts per hundred parts of) or higher. The response of the nanocomposite under melt extension reveals an initial decrease in the melt strength and elongational viscosity with increasing clay concentration up to 6 phr. Later, the melt strength and elongational viscosity show slight increases with further increasing clay concentration. These results might be caused by a reduction in the molecular weight of the LCB‐PP matrix and by the intercalation of LCB‐PP molecular chains into the clay layers. Increases in the melt strength and elongational viscosity for the nanocomposites with decreasing extrusion temperature are also observed, which is due to flow‐induced crystallization under lower extrusion temperature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

In situ WAXS/SAXS structural evolution study during uniaxial stretching of poly(ethylene therephthalate) nanocomposites in solid state: Poly(ethylene therephthalate)/montmorillonite nanocomposites

This work investigates the solid state uniaxial stretching of neat polyethylene therephthalate, PET, and its montmorillonite, MMT, nanocomposites (0.3 wt % of MMT particles with different initial agglomerate sizes) showing intercalated and tactoid morphologies, followed by in situ WAXS and SAXS experiments under an X‐ray synchrotron source. The distinct nanocomposite morphologies were assessed by WAXS and transmission electron microscopy. The in situ WAXS experiments during stretching evaluated the evolution of phase's mass fractions and the average level of molecular orientation upon uniaxial deformation, and the in situ SAXS experiments assessed the evolution of craze‐like structures and void sizes. Multiscale structure evolution models are proposed and compared for neat PET and its nanocomposites. Main global mechanisms are identical although with distinct evolutions of phase mass fractions. Also craze‐like/voids structures evolve with distinct sizes. Intercalated MMT morphology induces an earlier formation of periodical mesophase, a retarded widening of craze‐like structures and the smallest void sizes.© 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Structural characterization of hydrophilic polymer blends/montmorillonite clay nanocomposites

The nanocomposite films comprising polymer blends of poly(vinyl alcohol) (PVA), poly(vinyl pyrrolidone) (PVP), poly(ethylene oxide) (PEO), and poly(ethylene glycol) (PEG) with montmorillonite (MMT) clay as nanofiller were prepared by aqueous solution casting method. The X‐ray diffraction studies of the PVA–x wt % MMT, (PVA–PVP)–x wt % MMT, (PVA–PEO)–x wt % MMT and (PVA–PEG)–x wt % MMT nanocomposites containing MMT concentrations x = 1, 2, 3, 5 and 10 wt % of the polymer weight were carried out in the angular range (2θ) of 3.8–30°. The values of MMT basal spacing d₀₀₁, expansion of clay gallery width W_cg, d‐spacing of polymer spherulite, crystallite size L and diffraction peak intensity I were determined for these nanocomposites. The values of structural parameters reveal that the linear chain PEO and PEG in the PVA blend based nanocomposites promote the amount of MMT intercalated structures, and these structures are found relatively higher for the (PVA–PEO)–x wt % MMT nanocomposites. It is observed that the presence of bulky ester‐side group in PVP backbone restricts its intercalation, whereas the adsorption behavior of PVP on the MMT nanosheets mainly results the MMT exfoliated structures in the (PVA–PVP)–x wt % MMT nanocomposites. The crystallinities of the PEO and PEG were found low due to their blending with PVA, which further decreased anomalously with the increase of MMT concentration in the nanocomposites. The decrease of polymer crystalline phase of these materials confirmed their suitability in preparation of novel solid polymer nanocomposite electrolytes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40617.     

Study on rheological behavior of polypropylene/clay nanocomposites

Polypropylene/montmorillonite nanocomposites (PPCN) were prepared by melt intercalation with maleic anhydride modified low isotactic polypropylene as the compatibilizer. The linear and nonlinear rheological properties of polypropylene/montmorillonite nanocomposites were studied. The deviation from linear behavior occurred at a strain of 10⁰ that was quite less than that for the polymer matrix. The results of dynamic frequency scan showed that the percolation threshold of PPCN was near 3 wt %. Having been subjected to steady preshear, the tactoids could be oriented preferentially in the shear direction, and the percolation network was ruptured. The magnitudes of the stress overshoots observed in the reverse flow experiments were strongly dependent on the rest time, which indicated that the ruptured network could be reorganized even under quiescent conditions. Furthermore, PPCN displayed a strain‐scaling stress response to the startup of steady shear. The maxima of the stress overshoots appeared at the stain of 10⁰, which was consistent with the strain where the deviation of linear viscoelastic behavior started. It might imply that subjected to the deformation less than 10⁰, the network structure could be regard as elastic one. Additionally, the analogous strain‐scaling stress response to the startup steady shear elucidated the structural analogy between PPCN and liquid crystal polymer solution. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3609–3617, 2003     

Synthesis of polypropylene/clay nanocomposites using bisupported Ziegler‐Natta catalyst

In this article, preparation of polypropylene/clay nanocomposites (PPCNC) via in situ polymerization is investigated. MgCl₂/montmorillonite bisupported Ziegler‐Natta catalyst was used to prepare PPCNC samples. Montmorillonite (MMT) was used as an inert support and reinforcement agent. The nanostructure of the composites was characterized by X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques. Obtained results showed that silica layers of the MMT in these PPCNC were intercalated, partially exfoliated, and uniformly dispersed in the polypropylene matrix. Thermogravimetric analysis showed good thermal stability for the prepared PPCNC. Differential scanning calorimetric was used to investigate both melting and crystallization temperatures, as well as the crystallinity of the PPCNC samples. Results of permeability analysis showed significant increase in barrier properties of PPCNC films. Effective parameters on molecular weight and flow ability of produced samples such as Al/Ti molar ratio and H₂ concentration were also investigated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

间规聚苯乙烯/等规聚丙烯共混物的热性能

用差示扫描量热法(DSC)、动态力学分析(DMA)和热重法(TGA)等研究了间规聚苯乙烯/等规聚丙烯(sPS/iPP)、sPS与聚-1-丁烯(B30)组成的嵌段共聚物和sPS/iPP/B30共混体系的热性能。结果表明sPS/iPP是不相容体系,B30与iPP可相容,B30可作为sPS/iPP共混物的相容剂。DSC和DMA分析结果表明,加入适量的B30时,sPS/iPP/B30共混物中iPP的玻璃化转变温度随B30加入量的增加而逐渐升高,而sPS的玻璃化转变温度则随B30加入量的增加而逐渐降低;TGA分析结果表明共混体系的热失重温度高于300℃,比iPP的高。     

Strain‐induced crystallization behavior of phenolic resin crosslinked natural rubber/clay nanocomposites

Nanocomposites of natural rubber (NR) and unmodified clay were prepared by latex compounding method. Phenolic resin (PhOH) was used to crosslink NR. Crosslinked neat NR was also prepared for comparison. The structure–property relationship of uncrosslinked and crosslinked NR/clay nanocomposites was examined to verify the reinforcement mechanism. Microstructure of NR/clay nanocomposites was studied by using transmission electron microscopic (TEM), X‐ray diffraction (XRD), wide angle X‐ray diffraction (WAXD), and small angle X‐ray scattering (SAXS) analyses. The results showed the evidence of intercalated clay together with clay tactoids for the nanocomposite samples. The highest tensile strength was achieved for the crosslinked NR/clay nanocomposite. The onset strain of deformation induced the crystallization of NR for nanocomposites was found at almost the same strain, and furthermore their crystallization was developed at lower strain than that of the crosslinked neat NR because of the clay orientation and alignment. However, at high strain region, the collaborative crystallization process related to the clay dispersion and conventional crosslink points in the NR was responsible to considerably high tensile strength of the crosslinked NR/clay nanocomposite. Based on these analyses, a mechanistic model for the strain‐induced crystallization and orientational evolution of a network structure of PhOH‐crosslinked NR/clay nanocomposite was proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42580.