Interfacial modification of single‐walled carbon nanotubes for high‐loading‐reinforced polypropylene composites

In this article, we present a strategy for fabricating polypropylene (PP)/polypropylene‐regrafted single‐walled carbon nanotube (PP‐re‐g‐SWNT) composites with a high loading of single‐walled carbon nanotubes (SWNTs; 20 wt %). The PP‐re‐g‐SWNTs were characterized by X‐ray photoelectron, Fourier transform infrared spectroscopy, transmission electron microscopy, and thermogravimetric analysis (TGA). The PP‐re‐g‐SWNTs showed excellent interfacial adhesion and dispersion. Furthermore, PP molecules, about 72 wt % by mass, were homogeneously bonded onto the surface of the SWNTs according to TGA. In this hybrid nanocomposite system, the PP‐re‐g‐SWNTs were covalently integrated into the PP matrix and became part of the conjugated network structure (as evidenced by differential scanning calorimetry and dynamic mechanical analysis) rather than just a separate component. Accordingly, the PP/PP‐re‐g‐SWNT composites presented obvious improvements in mechanical properties and conductivity (from 10^?10 to 10^?2). Most importantly, the tensile and flexural strength of the PP/PP‐re‐g‐SWNT composites did not exhibit an obvious downturn with the addition of 20 wt % SWNTs; this was contrary to documented results. We believe that these new observations were due to the novel structure of the PP‐re‐g‐SWNTs. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39817.     

Improvement of compatibility of poly(ethylene terephthalate) and poly(ethylene octene) blends by γ‐irradiation

Blends of poly(ethylene terephthalate) (PET) and poly(ethylene octene) (POE) were prepared by melt blending with various amounts of trimethylolpropane triacylate (TMPTA). The mechanical properties, phase morphologies, and gel fractions at various absorbed doses of γ‐irradiation have been investigated. It was found that the toughness of blends was enhanced effectively after irradiation as well as the tensile properties. The elongation at break for all studied PET/POE blends (POE being up to 15 wt %) with 2 wt % TMPTA reached 250–400% at most absorbed doses of γ‐irradiation, approximately 50–80 times of those of untreated PET/POE blends. The impact strength of PET/POE (85/15 wt/wt) blends with 2 wt % TMPTA irradiated with as little as 30 kGy absorbed dose exceeded 17 kJ/m², being approximately 3.4 times of those of untreated blends. The improvement of the mechanical properties was supported by the morphology changes. Scanning electron microscope images of fracture surfaces showed a smaller dispersed phase and more indistinct inter‐phase boundaries in the irradiated blends. This indicates increased compatibility of PET and POE in the PET/POE blends. The changes of the morphologies and the enhancement of the mechanical properties were ascribed to the enhanced inter‐phase boundaries by the formation of complex graft structures confirmed by the results of the gelation extraction and Fourier Transform Infrared analyses. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermoplastic elastomers derived from bio‐based monomers

Series of copolyesters based on poly(propylene succinate) (PPS) and poly(butylene succinate) (PBS), which can be produced from biological feedstock, and postconsumer poly(ethylene terephthalate) (PET) were synthesized with the aim of developing sustainable materials, which combine the mechanical properties of high performance elastomers with those of flexible plastics. The aliphatic polyesters were synthesized by the catalyzed two‐step transesterification reaction of dimethyl succinate, 1,3‐propanediol, and 1,4‐butanediol followed by melt reaction with PET in bulk. The content of PET segments in the polymer chains was varied from about 10 to 100 wt % per 100 wt % PPS or PBS. The effect of the introduction of the PET segments on the structure, thermal, physical, and mechanical properties was investigated. The composition and structure of these aliphatic/aromatic copolyesters were determined by NMR spectroscopy. The thermal properties were investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The level of crystallinity was studied by means of DSC and wide‐angle X‐ray scattering. A depression of melting temperature and a reduction of crystallinity of copolyesters with increasing content of PET segments were observed. Consequently, the tensile modulus and strength of copolyesters decreased, and the elongation at break increased with PET content in the range of 10?50 wt %. Thus, depending on PET content, the properties of copolyesters can be tuned ranging from semicrystalline polymers possessing good tensile modulus (380 MPa) and strength (24 MPa) to nearly amorphous polymer of high elongation (～800%), and therefore they may find applications in thermoplastics as well as elastomers or impact modifiers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39815.     

Preparation and properties of the single‐walled carbon nanotube/cellulose nanocomposites using N‐methylmorpholine‐N‐oxide monohydrate

Single‐walled carbon nanotube (SWNT)/cellulose nanocomposite films were prepared using N‐methylmorpholine‐N‐oxide (NMMO) monohydrate as a dispersing agent for the acid‐treated SWNTs (A‐SWNTs) as well as a cellulose solvent. The A‐SWNTs were dispersed in both NMMO monohydrate and the nanocomposite film (as confirmed by scanning electron microscopy) because of the strong hydrogen bonds of the A‐SWNTs with NMMO and cellulose. The mechanical properties, thermal properties, and electric conductivity of the nanocomposite films were improved by adding a small amount of the A‐SWNTs to the cellulose. For example, by adding 1 wt % of the A‐SWNTs to the cellulose, tensile strain at break point, Young's modulus, and toughness increased ～ 5.4, ～ 2.2, and ～ 6 times, respectively, the degradation temperature increased to 9°C as compared with those of the pure cellulose film, and the electric conductivities at ? (the wt % of A‐SWNTs in the composite) = 1 and 9 were 4.97 × 10^?4 and 3.74 × 10^?2 S/cm, respectively. Thus, the A‐SWNT/cellulose nanocomposites are a promising material and can be used for many applications, such as toughened Lyocell fibers, transparent electrodes, and soforth. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

PET-SWNT Nanocomposite Fibers through Melt Spinning

Poly(ethylene terephthalate)-single-walled carbon nanotube (PET-SWNT) nanocomposite fibers have been prepared through melt spinning and drawing. While acting as effective nucleating agents for PET melt crystallization, SWNTs also provide significant reinforcement to PET fibers. For example, the tenacity and initial modulus of the composite fiber with 1 wt% SWNTs were, respectively, 1.8 times and 3.2 times higher as compared to those of the pristine PET fiber prepared under identical conditions. When the draw ratio was increased, tenacity and modulus of the fibers increased, indicating that drawing induced orientation of the polymer molecules and SWNTs. Thermal stability of the fibers was not significantly affected by the presence of SWNTs at low concentrations.     

Multiwall‐carbon‐nanotube‐reinforced poly(ethylene terephthalate) nanocomposites by melt compounding

Poly(ethylene terephthalate) (PET) nanocomposites reinforced with multiwall carbon nanotubes (MWCNTs) were prepared through melt compounding in a twin‐screw extruder. The presence of MWCNTs, which acted as good nucleating agents, enhanced the crystallization of PET through heterogeneous nucleation. The incorporation of a small quantity of MWCNTs improved the thermal stability of the PET/MWCNT nanocomposites. The mechanical properties of the PET/MWCNT nanocomposites increased with even a small quantity of MWCNTs. There was a significant dependence of the rheological properties of the PET/MWCNT nanocomposites on the MWCNT content. The MWCNT loading increased the shear‐thinning nature of the polymer‐nanocomposite melt. The storage modulus and loss modulus of the PET/MWCNT nanocomposites increased with increasing frequency, and this increment effect was more pronounced at lower frequencies. At higher MWCNT contents, the dominant nanotube–nanotube interactions led to the formation of interconnected or networklike structures of MWCNTs in the PET/MWCNT nanocomposites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1450–1457, 2007     

Carbon nanotubes induced crystallization of poly(ethylene terephthalate)

We have investigated the crystallization characteristics of melt compounded nanocomposites of poly(ethylene terephthalate) (PET) and single walled carbon nanotubes (SWNTs). Differential scanning calorimetry studies showed that SWNTs at weight fractions as low as 0.03 wt% enhance the rate of crystallization in PET, as the cooling nanocomposite melt crystallizes at a temperature 10 °C higher as compared to neat PET. Isothermal crystallization studies also revealed that SWNTs significantly accelerate the crystallization process. WAXD showed oriented crystallization of PET induced by oriented SWNTs in a randomized PET melt, indicating the role of SWNTs as nucleating sites.     

Crystallization behavior and mechanical properties of bio‐based green composites based on poly(L‐lactide) and kenaf fiber

Bio‐based polymer composite was successfully fabricated from plant‐derived kenaf fiber (KF) and renewable resource‐based biodegradable polyester, poly(L ‐lactide) (PLLA), by melt‐mixing technique. The effect of the KF weight contents (0, 10, 20, and 30 wt %) on crystallization behavior, composite morphology, mechanical, and dynamic mechanical properties of PLLA/KF composites were investigated. It was found that the incorporation of KF significantly improves the crystallization rate and tensile and storage modulus. The crystallization of PLLA can be completed during the cooling process from the melt at 5°C/min with the addition of 10 wt % KF. It was also observed that the nucleation density increases dramatically and the spherulite size drops greatly in the isothermal crystallization with the presence of KF. In addition, with the incorporation of 30 wt % KF, the half times of isothermal crystallization at 120°C and 140°C were reduced to 46.5% and 28.1% of the pure PLLA, respectively. Moreover, the tensile and storage modulus of the composite are improved by 30% and 28%, respectively, by the reinforcement with 30% KF. Scanning electron microscopy observation also showed that the crystallization rate and mechanical properties could be further improved by optimizing the interfacial interaction and compatibility between the KF and PLLA matrix. Overall, it was concluded that the KF could be the potential and promising filler for PLLA to produce biodegradable composite materials, owing to its good ability to improve the mechanical properties as well as to accelerate the crystallization of PLLA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Morphology and thermomechanical properties of recycled PET–organoclay nanocomposites

Recycled PET/organoclay nanocomposites were prepared by melt intercalation process with several amounts (1, 3, and 5 wt %) of clay modified with quaternary ammonium salt (DELLITE 67G) dispersed in a recycled poly(ethylene terephthalate) (rPET) matrix. The resultant mechanical properties (modulus and yield strength) of the nanocomposites were found to be different from those of rPET. Wide angle X‐ray scattering (WAXS) and Transmission Electron Microscopy (TEM) measurements have shown that although complete exfoliation was not achieved, delaminated clay platelets could be observed. Thermal analysis did not show significant changes in the thermal properties from those of recycled PET. Mechanical testing showed that nanocomposite properties were superior to the recycled PET in terms of strength and elasticity modulus. This improvement was attributed to nanoscale effects and strong interaction between the rPET matrix and the clay interface, as revealed by WAXS and TEM. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1839–1844, 2007     

Hybrid clay‐carbon nanotube/PET composites: Preparation,processing, and analysis of physical properties

The aim of this work was the preparation of novel composites of poly(ethylene terephthalate) (PET) and nano‐hybrid systems based on clay used as catalyst for the growth of multi walled carbon nanotubes (Clay‐CNTs), through catalytic chemical vapor deposition (CCVD). The carbon content into the hybrid filler was 58.1 wt %. Composites with 1.0, 1.5, 2.0, 3.0 wt % of Clay–CNTs were obtained by melt compounding and processed using a microinjection molding press. Unfilled PET was processed in the same composites conditions. Structural characterization and physical properties (thermal, degradation, mechanical, and electrical) were analyzed and correlated to the hybrid filler loading, and carbon nanotubes amount. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40441.     

Expanding the application field of post‐consumer poly(ethylene terephthalate) through structural modification by reactive blending

With the aim of up‐grading the material properties of post‐consumer PET, making them suitable for extrusion of thermoformable thick sheets, a series of polyepoxy chain extenders have been comparatively evaluated as melt viscosity modifiers for a toughened compatibilized blend containing up to 80 wt % of bottle‐grade post‐consumer recycled poly(ethylene terephtalate) (r‐PET). Combinations of a commercial modifier with pentaerythritol were also successfully employed to cause simultaneous hyperbranching and controlled chain scission, thereby modifying the melt rheology of the material without excessively increasing the molecular weight, as highlighted by common technological melt viscosity measurements such as online torque and off‐line melt flow rate (MFR). Since the high melt fluidity of PET plays a critical role on its flame resistance, the combined effect of chain extenders and halogen‐free phosphorated additives on the fire resistance of the modified toughened blends was also investigated. Preliminary results indicate that the chemical reactions among polymer and additives must be taken into careful account to prevent unfavorable effects on the ultimate melt rheology and mechanical properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40881.     

Recycled PET‐organoclay nanocomposites with enhanced processing properties and thermal stability

Preparation of thermally stable recycled PET‐organoclay nanocomposites with improved processing and mechanical properties is a challenging task from the environmental as well as industrial and commercial point of view. In this work, both modification of sodium‐type montmorillonite with 1,2‐dimethyl‐3‐octadecyl‐1H‐imidazol‐3‐ium chloride and additional treatment with [3‐(glycidyloxy)propyl]trimethoxysilane was performed. Thermal stability of the organoclays and nanocomposites prepared by melt compounding was tested by thermogravimetric analysis, differential scanning calorimetry, and melt rheology. In comparison with the organoclays modified with quaternary ammonium compounds, the prepared clays showed substantial suppression of matrix degradation during melt mixing. The increase in interlayer distance of silicate platelets and homogeneity of dispersions in the recycled and virgin PET matrices have been evaluated by transmission electron microscopy and wide‐angle X‐ray scattering. The higher degree of delamination in the nanocomposites filled with imidazole organoclays was in a good agreement with improved rheological characteristics and led to significant enhancement in mechanical properties and thermal stability. A difference in structure (besides the level of delamination and homogeneity of silicate platelets) of recycled versus virgin PET nanocomposites was detected by X‐ray diffraction patterns. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Alumina‐filled polystyrene micro‐ and nanocomposites prepared by melt mixing with and without latex precompounding: Structure and properties

Alumina fillers were incorporated in polystyrene (PS) in 4.5 wt % by melt blending with and without latex precompounding. Latex precompounding was used for the latex‐mediated predispersion of the alumina particles. The related masterbatch was produced by mixing PS latex with water dispersible boehmite alumina in various particle sizes followed by drying. The dispersion of the alumina in the PS was studied by transmission and scanning electron microscopy (TEM and SEM, respectively). The mechanical and thermomechanical properties of the PS composites were determined in uniaxial tensile, dynamic‐mechanical thermal analysis (DMTA), and short‐time creep tests performed at various temperatures. In addition, the melt flow of the composites was characterized in a plate/plate rheometer. It was found that direct melt mixing of the alumina with PS resulted in micro‐, whereas the masterbatch technique in nanocomposites. The stiffness and resistance to creep (summarized in master curves) of the nanocomposites were improved compared to those of the microcomposites. The properties of the composites were upgraded by decreasing nominal size of the water dispersible alumina. The preparation technique and the size of the alumina particles affected the tensile strength, melt viscosity, and heat distortion temperature in lesser extent than the stiffness and thus compliance data. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effects of extrusion conditions on the properties of recycled poly(ethylene terephthalate)/nanoclay nanocomposites prepared by a twin‐screw extruder

The effects of extrusion conditions on the mechanical properties of recycled poly(ethylene terephthalate) (rPET)/clay nanocomposites were studied. Nanocomposites of recycled PET containing 2.5 and 5.0 wt % of montmorillonite modified with organophilic quaternary ammonium salt (DELLITE 67G) were prepared by melt compounding using a corotating twin‐screw type extruder at two different screw rotation speeds: 250 and 150 rpm. The highest value of Young's modulus was found for low screw rotation speed (150 rpm). Morphological analysis using transmission electron microscopy (TEM) revealed the presence of fully exfoliated clay platelets in samples prepared at 150 rpm. It was concluded that the screw rotation speed should be optimized when preparing recycled PET/clay nanocomposites by melt compounding. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Surface modification of single‐walled carbon nanotubes with polyethylene via in situ Ziegler–Natta polymerization

Single‐walled carbon nanotubes (SWNTs) were modified with polyethylene (PE) prepared by in situ Ziegler–Natta polymerization. Because of the catalyst pretreated on the surface of the SWNTs, the ethylene was expected to polymerize there. Scanning electron microscopy images and solubility measurements showed that the surface of the SWNTs was covered with a PE layer, and a crosslink may have formed between the SWNTs and PE. When the SWNTs covered with a PE layer were mixed with commercialized PE by melt blending, the resulting composite had better mechanical properties than the composite from the SWNTs without a PE layer. The yield strength, the tensile strength and modulus, the strain at break, and the fracture energy of the modified‐SWNT/PE composites were improved by 25, 15.2, 25.4, 21, and 38% in comparison with those of the raw‐SWNT/PE composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3697–3700, 2004     

PET/PP blending by using PP‐g‐MA synthesized by solid phase

In attempts to improve the compatibility of polypropylene (PP) with polyethylene terephthalate (PET), a maleic anhydride grafted PP (PP‐g‐MA) was evaluated as a compatibilizer in a blend of 30/70 wt % PP/PET. PP‐g‐MA was produced from isotactic homopolymer PP utilizing the technique of solid phase graft copolymerization. Qualitative confirmations of the grafting were made by Fourier transform infrared spectroscopy (FTIR). Three different weight percent of compatibilizer, PP‐g‐MA, i.e., 5, 10, and 15 wt % have been used in PP/PET blends. The compatibilizing efficiency for PP/PET blend was examined using differential scanning calorimetry (DSC), optical microscopy (OM), scanning electron microscopy (SEM) of crycrofractured surfaces, and energy dispersive X‐ray spectrum (EDAX). The results show that the grafted PP promotes a fine dispersed phase morphology, improves processability, and modifies the crystallization behavior of the polyester component. These effects are attributed to enhance phase interaction resulting in reduced interfacial tension. Also, the results show that the compatibilizing effects of the three amounts of grafted PP in blend are different and dependent on the amount used. Adding 10 wt % of compatibilizer into blend produced the finest dispersed morphology. Elemental analysis results show that PP is matrix. DSC determination revealed that the melting temperature (T_m) of the PET component declined to some extent by comparison with neat PET. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104, 3986–3993, 2007     

Characterization of PET nanocomposites produced by different melt‐based production methods

Poly(ethylene terephthalate) (PET) based nanocomposites containing 3 wt % of different nanoparticles (MontMorilloniTe–MMT; titanium dioxide–TiO₂; and silica dioxide–SiO₂) were prepared via two independent procedures: mechanical mixing with subsequent direct injection molding (DIM) and mechanical mixing, followed by extrusion blending and injection molding (EIM). The contributions of nanofillers with respect to pure PET were evaluated. The incorporation of nanofillers reduces the intrinsic viscosity of the polymer matrix when processed by DIM and EIM. SAXS results showed that: MMT layers were intercalated for both processing procedures, but slightly higher for EIM; a better dispersion with smaller agglomerates size is achieved for TiO₂ and SiO₂ nanoparticles for EIM than for DIM. According to the results of DSC analysis, all fillers behave as nucleating agents for PET except SiO₂ that acts as inhibitor in case of DIM procedure. The mechanical behavior was assessed in tensile testing. The mechanical test revealed that the addition of nanoparticles have a slight influence on the elastic modulus and yield stress, but a drastic negative influence on the deformation capabilities of the moldings. The measured optical properties of the moldings gloss and haze are also strongly affected by the presence of nanoparticles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Bottle‐to‐bottle recycling of PET via nanostructure formation by melt intercalation in twin screw compounder: Improved thermal,barrier, and microbiological properties

Attempts have been made to modify the properties of the injection processing‐scraped PET (denoted as RPET) via intercalation with different levels of organically modified nanoclay (montmorillonite) by melt blending in a corotating twin screw compounder. The clay platelets dispersion state has been qualitatively correlated with the melt linear viscoelastic as well as tensile and barrier properties of the prepared nanocomposites. Oxygen permeation of the nanocomposite PET films showed significant reduction compared with the pristine PET polymer. All the PET/nanoclay composites exhibited no bacterial growth, with no potentiality to generate acetaldehyde, as measured by GC/Mass analyzer. X‐ray diffractometry and transmission electron microscopy performed on the scraped PET/organoclay nanocomposite samples showed increase in d₀₀₁ spacing of the clay layers and their dispersion throughout the PET matrix. Differential scanning calorimetry analysis showed higher crystallization temperature as well as crystallization enthalpy (ΔH_c) for the nanocomposite samples, compared with the unprocessed virgin PET. The RPET nanocomposite samples composed of 3 and 5% of nanoclay exhibited enhanced melt elastic modulus and pseudosolid‐like behavior at low shear frequencies measured by rheomechanical spectroscopy than the unfilled pristine‐scraped PET, indicating the formation of nanoscopic network structure by the clay platelets, which leads to the development of nanostructured resin. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Comparative effect of metallocene and Ziegler‐Natta polypropylene on the exfoliation of montmorillonite and hectorite clays to obtain nanocomposites

The present study was carried out on the effect of molecular weight and polydispersity of polypropylene (PP) obtained via Ziegler‐Natta or metallocene catalysis on the formation of nanocomposites with montmorillonite and mineral and synthetic hectorite. The formation of the nanocomposites was achieved by the melt‐mix method. X‐ray diffraction, transmission electron microscopy, and analysis of mechanical properties showed that, using PP obtained via metallocene catalysis (polydispersity ～ 2), it is possible to achieve improved formation of nanocomposites compared with PP obtained via Ziegler‐Natta catalysis (polydispersity ～ 4). It was also found that the molecular weight of the PP affects the tendency toward clay exfoliation and consequently the properties of the nanocomposites. Montmorillonite type clay was evaluated at 1%, 3%, and 5% by weight in the nanocomposite. The nanocomposite with 1 wt % clay was found to have better mechanical properties compared with the nanocomposite containing 3 wt % and 5 wt %. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 698–706, 2007     

Polypropylene–clay blends compatibilized with MAH‐g‐POE

A series of new Polypropylene (PP)–clay blends, containing 5 wt % clay, were prepared by melt compounding with maleic anhydride grafted poly(ethylene‐co‐octene) (MAH‐g‐POE) as the compatibilizer by varying its content from 0 to 20 wt %. The effect of MAH‐g‐POE on the PP–clay miscibility was examined by X‐ray diffraction (XRD), scanning electronic microscope (SEM) observation, differential scanning calorimeter (DSC) analysis, dynamic mechanical thermal analysis (DMTA), and rheological testing in sequence. The results showed that the addition of MAH‐g‐POE could improve the dispersion of clay layers in PP matrix and promoted the interaction between PP molecules and clay layers. At 10 wt % MAH‐g‐POE, the PP–clay blend exhibited a highest value of Tc,onset and Tg as well as a biggest melt storage modulus (G′), indicating the greatest PP–clay interaction. On the other hand, improved toughness and stiffness coexisted in blends with 5–10 wt % loading of MAH‐g‐POE. In view of SEM and DMTA observations, MAH‐g‐POE was well miscible with the PP matrix, even with the concentration up to 20 wt %. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 2558–2564, 2006