Direct Melt Blending Research Articles

Flammability and tensile properties of polylactide nanocomposites with short carbon fibers

Nanocomposites of polylactide (PLA) with aluminum hydroxide (ATH), short carbon fibers (CF), and montmorillonite (MMT) were prepared via direct melt blending. The exfoliated and intercalated clay structures with some aggregations in the PLA matrix were observed. The tensile strength and elongation at break of the PLA composite caused by the high content of the retardant ATH were improved by adding modified MMT and CF to replace a portion of ATH in the PLA matrix. The thermal degradation temperatures and char residue of the PLA/ATH/MMT/CF nanocomposites as determined by thermogravimetric analysis were higher than without MMT. Furthermore, a novel method was proposed to analyze the flammability of composite using an infrared camera, which could capture the apparent thermal image of the sample during UL 94 V test. It was found that, with addition of the MMT and short CF, a more effective insulation layer could be formed on the ablating surface of the PLA/ATH composite, and the high thermal conductivity of the CF might increase the release rate of heat from the surface composite during burn, thus the PLA/ATH/MMT nanocomposite containing short carbon fibers having a V-0 rating without flaming dripping could be obtained.

Enhanced electrical properties of polycarbonate/carbon nanotube nanocomposites prepared by a supercritical carbon dioxide aided melt blending method

Polycarbonate/carbon nanotube (CNT) nanocomposites were generated using a supercritical carbon dioxide (scCO2) aided melt blending method, yielding nanocomposites with enhanced electrical properties and improved dispersion while maintaining the aspect ratio of the as-received CNTs. Baytubes® C 150 P CNTs were benignly deagglomerated with scCO2 resulting in 5 fold (5X), 10X and 15X decreases in bulk density from the as-received CNTs. This was followed by melt compounding with polycarbonate to generate the CNT nanocomposites. Electrical percolation thresholds were realized at CNT loading levels as low as 0.83 wt% for composites prepared with 15X CNT using the scCO2 aided melt blending method. By comparison, a concentration of 1.5 wt% was required without scCO2 processing. Optical microscopy, transmission electron microscopy, and rheology were used to investigate the dispersion and mechanical network of CNTs in the nanocomposites. The dispersion of CNTs generally improved with scCO2 processing compared to direct melt blending, but was significantly worse than that of twin screw melt compounded nanocomposites reported in the literature. A rheologically percolated network was observed near the electrical percolation of the nanocomposites. The importance of maintaining longer carbon nanotubes during nanocomposite processing rather than focusing on dispersion alone is highlighted in the current efforts.

Effect of montmorillonite on carboxylated styrene butadiene rubber/hindered phenol damping material with improved extraction resistance

Three methods of blending, including direct blending, melt blending and latex blending, were introduced to disperse sodium based montmorillonite (Na-MMT) and N,N′-hexane-1,6-diylbis{3-(5-di-tert-butyl-4-hydroxyphenyl-propionamide)} (HP1098) into the carboxylated styrene butadiene (XSBR) matrix. Small angle X-ray Diffraction testing indicated that melting Na-MMT with HP1098 enlarged the d-spacing of Na-MMT, which was further enlarged by mechanical blending with XSBR, and this led to homogeneous dispersion of Na-MMT and HP1098, which was indicated by Transmission Electronic Microscopy; latex blending was found most advantageous in dispersing HP1098 which was essential for improved damping performance. Dynamic Mechanical Analysis was utilized to characterize damping properties, and enhanced static mechanical properties were presumably originated from molecule chains being intercalated into the enlarged galleries of Na-MMT by mechanical blending. Formation of hydrogen bonds was observed by Fourier Transformation Infrared Spectrum and was supposed to be responsible for exceptional damping performance at elevated temperature. Extraction measurement of XSBR/Na-MMT/HP1098 composite indicated that XSBR and Na-MMT showed synergic effect in protecting HP1098 molecules from being extracted, which is a promising method in preparing rubber/hindered phenol damping materials with improved extraction resistance, whereby increasing the performance stability and lifespan of the composite materials. Additional advantage of this type of materials is better processability and shortened vulcanization process.

Structure/transport property relationships within nanoclay-filled polyurethane materials using polycaprolactone-based masterbatches

Abstract The lamellar structure of montmorillonite (MMT) clays exhibits an interesting potential to improve the barrier properties of thermoplastic polyurethanes (TPU). However direct melt blending of an ester-based TPU and functional organoclays, despite showing good filler dispersion, did not allowed for improving neither barrier properties (i.e., sorption and diffusion to water vapor) not mechanical performances with respect to the unfilled TPU. Therefore, two alternative strategies involving poly(e-caprolactone) (PCL)/organoclay masterbatches were explored to investigate the possibility to prepare materials with improved mechanical and barrier properties. In the first strategy, a PCL/organoclay masterbatch with high inorganic content was obtained by melt-blending (coined “free PCL” masterbatch), whereas in the second strategy PCL-grafted organoclay nanohybrids, also with high inorganic content were synthesized by in situ intercalative grafting/ring-opening polymerization of e-caprolactone (CL). Purposely, ROP of CL was initiated from hydroxyl groups available onto the MMT surface actually organo-modified by alkylammonium cations bearing hydroxyl functions (coined “nanohybrid PCL” masterbatch). These highly-filled PCL masterbatches (with ca. 25 wt% in inorganics) were then added into the ester-based TPU to prepare nanoclay/polyurethane nanocomposites by melt-blending. The morphology and dispersion of the resulting materials were characterized by X-ray diffraction and transmission electron microscopy. Improved sorption and diffusion properties towards water vapor as well as mechanical properties were measured. Herein, these results are discussed as a function of both clay dispersion and matrix/organoclay interaction.

The Effect of Natural Rubber Toughening on Mechanical Properties of Poly(lactic Acid)/Multiwalled Carbon Nanotube Nanocomposite

nvestigation was done on the use of natural rubber (NR) as impact modifier in polylactic acid (PLA) nanocomposite containing carboxylic functionalized multiwalled carbon nanotubes (MWCNT) as nanofillers. NR toughened PLA nancomposite consisting of 1 phr MWCNT and NR contents varies from 5 to 20 wt% were prepared by direct melt blending in a counter-rotating twin-screw extruder followed by injection moulding into test specimens for mechanical properties analysis. The tensile, flexural and impact test analysis were carried out to investigate the mechanical properties of PLA/NR/MWCNT nanocomposites at different loading of NR. As comparison, pure PLA, PLA/NR with 5 wt% NR and PLA/MWCNT with 1 phr nanotubes were also prepared with similar method. Results indicated that introduction of NR into PLA/MWCNT contributed to significant improvement in impact strength and ductility of the nanocomposite. Moreover, the deterioration effect of nancomposites stiffness, mechanical and flexural strength due to the introduction of NR was minimized with the presence of MWCNT in the nanocomposite system.

Effect of nanosilica on the morphology of polyethylene investigated by AFM

Abstract Nanocomposites from low density polyethylene (PE) and nanosilica (NS) with and without a compatibilizer were prepared via direct melt blending. Their morphology and mechanical properties were investigated in relation to that of neat PE using peak force QNM (quantitative nanomechanics) analysis. A suppression of spherulitic development as compared to neat PE was observed in PE/NS nanocomposites. NS induced no modification in the lamellar thickness of PE but a slight decrease of the crystallinity was detected. Changes in the thickness and distribution of the amorphous strips were emphasized in samples containing the compatibilizer. For the first time the nanomechanical properties of PE–NS interface were quantitatively characterized. AFM investigation of fractured samples revealed different mechanisms involved in deformation and breaking of neat PE and composites.

Cross-linking of a novel reactive polymeric intumescent flame retardant to ABS copolymer and its flame retardancy properties

In this work, a reactive polymeric intumescent flame retardant (PDSPB) was synthesized and applied to ABS resin. The flame retarded materials were prepared by direct melt blending of ABS and PDSPB (ABS/PDSPB), as well as melt cross-linking of PDSPB to ABS (ABS-c-PDSPB). The cross-linking reaction was characterized by fourier transform infrared spectrometry (FTIR) and gel content measurement. The thermal stability, flame retardancy, carbonization chemistry and dynamic mechanical properties were investigated by TGA, dynamic FTIR, SEM, CONE calorimetry and dynamic mechanical analysis (DMA). The results showed that the addition of PDSPB can effectively reduce the flammability properties including peak heat release rate (PHRR), total heat release (THR) and average mass loss rate (AMLR). An improvement of the limited oxygen index value was also observed. Especially, the cross-linking of PDSPB can improve the ignition time and reduce THR during combustion. Moreover, ABS-c-PDSPB displayed a more obvious intumescent char layer and char weight than that of ABS/PDSPB blends. Furthermore, cross-linking of PDSPB enhanced the thermal stability and considerably delayed the thermal oxidation degradation of ABS. The dynamic mechanical properties were improved and the plasticization effect was reduced by cross-linking of PDSPB.

Using supercritical carbon dioxide in preparing carbon nanotube nanocomposite: Improved dispersion and mechanical properties

AbstractImprovements in carbon nanotube (CNT) dispersion and subsequent mechanical properties of CNT/poly(phenylsulfone) (PPSF) composites were obtained by applying the supercritical CO2 (scCO2)‐aided melt‐blending technique that has been used in our laboratory for nanoclay/polymer composite preparation. The preparation process relied on rapid expansion of the CNTs followed by melt blending using a single‐screw extruder. Scanning electronic microscopy results revealed that the CNTs exposed to scCO2 at certain pressures, temperatures, exposure time, and depressurization rates have a more dispersed structure. Microscopy results showed improved CNT dispersion in the polymer matrix and more uniform networks formed with the use of scCO2, which indicated that CO2‐expanded CNTs are easier to disperse into the polymer matrix during the blending procedure. The CNT/PPSF composites prepared with scCO2‐aided melt blending and conventional melt blending showed similar tensile strength and elongation at break. The Young's modulus of the composite prepared by means of conventional direct melt blending failed to increase beyond the addition of 1 wt% CNT, but the scCO2‐aided melt‐blending method provided continuous improvements in Young's modulus up to the addition of 7 wt% CNT. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Impact‐modified polylactide–calcium sulfate composites: Structure and properties

AbstractThe objective of the study is the preparation and comprehensive characterization of novel high performance polylactide (PLA)‐based composites designed with specific impact properties. Highly filled composites were obtained by melt‐blending PLA and 40 wt % anhydrite II (AII) microfiller, the dehydrated form of calcium sulfate hemihydrate, a by‐product having as origin the lactic acid (LA) fabrication process. The toughness of PLA–AII composites was improved by addition of a selected impact modifier (IM) based on ethylene–acrylate copolymer (Biomax® Strong 100, noted BS). PLA–AII composites containing (10 wt %) BS were prepared using two procedures: (1) the direct melt blending of all components in a single step and (2) the previously coating of AII by BS, followed by mixing of coated filler with PLA. These approaches were carried out to modify the phase structure and to determine their influence on the final composite properties. As reference samples, PLA and PLA–BS blends were accounted. The miscibility and phase morphology (differential scanning calorimetry and scanning electron microscopy), thermal stability (thermogravimetric analysis), and thermomechanical properties (DMTA, tensile, and impact tests) were investigated to explain the toughening mechanism in the BS‐modified composites. Noticeable, an attractive threefold increase of impact strength with respect to the composite without modifier and remarkable thermomechanical performances were assessed. The composite obtained using BS‐coated AII showed better properties (e.g., impact strength of 5.4 kJ/m2), improvements ascribed to the good filler dispersion and effective modification of interfacial regions (PLA–filler) by the BS‐layer. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Microstructure and mechanical properties of polypropylene/poly (ethylene-co-octene copolymer)/clay ternary nanocomposites prepared by melt blending using supercritical carbon dioxide as a processing aid

To improve the mechanical properties of polypropylene (PP), poly (ethylene-co-octene copolymer) (PEOc) and clay particles were incorporated by melt blending with the aid of supercritical carbon dioxide. Results from X-ray diffraction, electron microscopy, and rheology show that using sc-CO2 makes the clay layers mainly intercalated by polymer chains and well exfoliate in the nanocomposites relative to direct melt blending. This leads to a three-dimensional network structure formed in the nanocomposites as confirmed by rheology. Evidences from scanning electron microscope (SEM) indicate most of clay particles are mainly localized close to or inside the PEOc phase and others disperse separately in the PP phase. The incorporation of PEOc and clay significantly improve the impact strength of PP without the expense of lowering PP’s stiffness and strength. The use of sc-CO2 or PP-g-MA during melt-compounding can further improve the mechanical properties of the ternary nanocomposites. Compared to PP-g-MA, sc-CO2 is more favorable for dispersing clay in PP/PEOc blend and improving the mechanical properties of the nanocomposites.

Preparation and characterization of linear low‐density polyethylene/dickite nanocomposites prepared by the direct melt blending of linear low‐density polyethylene with exfoliated dickite

AbstractDickite particles were exfoliated by the thermal decomposition of molecular urea in the interlayer of dickite. The exfoliated dickite (ED) was composed with linear low‐density polyethylene (LLDPE) to prepare a novel LLDPE/dickite nanocomposite (LDN‐5). X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to evaluate the exfoliation effect. FTIR spectra showed that the inner‐surface hydroxyls of dickite decreased because of the sufficient exfoliation of the dickite layers. The 001 diffraction of dickite in the XRD pattern almost disappeared after exfoliation; this indicated the random orientation of dickite platelets. SEM and TEM micrographs confirmed the effective thermal decomposition of the interlamellar molecular urea ED layers, which resulted in smaller particle sizes and better dispersions of dickite in the resulting LLDPE/dickite composite. The microstructure of LDN‐5 showed that most of the dickite platelets were exfoliated and homogeneously dispersed in the LLDPE; this led to increases in the anticorrosion properties and thermal stabilities of LDN‐5. The results of salt‐spray tests illustrated that the corrosion rate of the iron coupon decreased from 23% (LLDPE packing) to 0.4% (LDN‐5 packing). Moreover, the thermal degradation temperature corresponding to a mass loss of 10% increased from 330°C (pure LLDPE) to 379°C (LDN‐5). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Thermal and mechanical properties of poly(ether ester)-based thermoplastic elastomer composites filled with TiO2 nanoparticles

Poly(butylene terephthalate)-block-poly(tetramethylene glycol) (PBT-PTMG)-based thermoplastic elastomer (TPE) was filled with nano TiO2 particles by direct melt blending. The particle content in matrix was varied from 1.3 to 4.9 vol.%. The samples were characterized using SEM, μCT, DSC, TGA, DMTA and tensile test. SEM examination shows strong interfacial interactions between TPE matrix and TiO2 particles due to formation of chemical bonds. The incorporation of TiO2 particles increases overall the thermal properties of soft and hard segments such as the glass transition temperature, the melting temperature, and the thermal stability of material. The tensile properties of TPE are also significantly improved indicated by increased tensile strength and modulus. Increasing particle content leads to increased mechanical properties and thermal stability of composites.

Study of the viscoelastic properties of PC/ABS blend containing triphenyl phosphate and nanoclay and its correlation with morphology

AbstractIn this study, the effect of triphenyl phosphate (TPP), commonly used as flame retardant, also montmorillonite nanoclay and hybrid of them, on the morphology and rheological characteristic of PC/ABS (Polycarbonate/Acrylonitrile–butadiene–Styrene) blends are investigated. The blends were prepared via a direct melt blending process in a twin‐screw extruder. Morphological properties were characterized by scanning electron microscopy, X‐ray diffraction, and transmission electron microscopy. The results for the variations of complex viscosity (η*) with angular frequency (ω) showed a good agreement with those obtained from Carreau model.A plateau modulus (G°N) was observed in the blends containing nanoclay, indicating the formation of a network structure that increases the modulus as the results of the intercalation of silicate layers of nanoclay. The complex viscosity is increased with the inclusion of nanoclay and TPP, but the effect is more evident with nanoclay. Also, the addition of nanoclay significantly enhances the non Newtonian behavior of PC/ABS blends, particularly at low‐frequencies. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Frequency and Temperature Dependences of Dielectric Dispersion and Electrical Properties of Polyvinylidene Fluoride/Expanded Graphite Composites

A conductive nanofiller, expanded graphite (EG), was introduced into polyvinylidene fluoride (PVDF) by direct melt blending process. The electrical conductivity and dielectric properties of resulting PVDF/EG composites were investigated in a wide range of frequencies from 102 to 108 Hz. The dielectric dispersion and conductivity of the composite system exhibited a strong frequency dependence particularly in the vicinity of percolation threshold (Φc = 6 vol%). Moreover, the dielectric permittivity tended to decrease with increasing frequency while the conductivity displayed a reverse trend. A large permittivity was found in the composite having EG content near Φc. Accordingly, percolation concept and biased random walk approach can be used to describe the carrier transport of percolating PVDF/EG system. The conductivity and permittivity of percolating PVDF/EG composites were observed to be temperature dependent.

Improving the exfoliation of layered silicate in a poly(ethylene terephthalate) matrix using supercritical carbon dioxide

AbstractA technique for improving the exfoliation of organically modified layered silicate (OMLS) in a poly(ethylene terephthalate) (PET) matrix using super critical carbon dioxide (scCO2) is compared to traditional direct melt blending. The process relies on the rapid expansion of a scCO2/OMLS mixture directly into the second stage of a single screw extruder where the clay and scCO2 mixture is subsequently melt blended with the PET matrix. The simple, environmentally benign process results in a more highly delaminated system than traditional direct melt compounding. X‐ray diffraction analysis is used to reveal improved clay morphologies and the resulting mechanical properties are examined. Rheology is used as a tool to draw conclusions about the effect that scCO2 has on reducing PET matrix degradation during processing. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Structure and Mechanical Properties of Polycarbonate Modified Clay Nanocomposites

Polycarbonate (PC)/modified clay nanocomposites were prepared, in the absence and presence of different amounts of maleic anhydride grafted polypropylene (PP-g-MA), by direct melt blending. Their structures, as well as mechanical, morphological and thermal properties, were characterized by X-ray diffractometry (XRD), tensile testing, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The XRD results of the PC/clay nanocomposites showed that they had intercalated structures, although some exfoliation was visible at low clay contents, that the gallery heights of the PC/clay nanocomposites were almost the same, and that some of the clay layers collapsed as a result of modifier decomposition at the high processing temperature. The XRD patterns of the PC/PP-g-MA/clay nanocomposites clearly show less intercalation and more exfoliation with increasing PP-g-MA content. These results were supported by TEM observations. Both the tensile strength and modulus show substantial improvements with both increasing clay and PP-g-MA contents, while the elongation at break substantially decreases, although the presence of PP-g-MA somewhat improves these values. All the nanocomposites have lower thermal stability than pure PC, but the presence of PP-g-MA seems to improve the thermal stability of these samples.

Structure and Mechanical Properties of Polycarbonate Modified Clay Nanocomposites

Polycarbonate (PC)/modified clay nanocomposites were prepared, in the absence and presence of different amounts of maleic anhydride grafted polypropylene (PP-g-MA), by direct melt blending. Their structures, as well as mechanical, morphological and thermal properties, were characterized by X-ray diffractometry (XRD), tensile testing, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The XRD results of the PC/clay nanocomposites showed that they had intercalated structures, although some exfoliation was visible at low clay contents, that the gallery heights of the PC/clay nanocomposites were almost the same, and that some of the clay layers collapsed as a result of modifier decomposition at the high processing temperature. The XRD patterns of the PC/PP-g-MA/clay nanocomposites clearly show less intercalation and more exfoliation with increasing PP-g-MA content. These results were supported by TEM observations. Both the tensile strength and modulus show substantial improvements with both increasing clay and PP-g-MA contents, while the elongation at break substantially decreases, although the presence of PP-g-MA somewhat improves these values. All the nanocomposites have lower thermal stability than pure PC, but the presence of PP-g-MA seems to improve the thermal stability of these samples.

Dispersion of nanoclay into polypropylene with carbon dioxide in the presence of maleated polypropylene

The effect of maleic anhydride grafted polypropylene (PP-g-MA) on the mechanical and rheological properties of polypropylene (PP)–clay nanocomposites prepared with nanoclay expanded with CO2 and direct melt blending was studied. The results from the studies of the mechanical properties, rheological properties, and transmission electron microscopy show that when PP-g-MA was combined with the technique that used CO2, greater enhancements in the mechanical properties and degree of dispersion of nanoclay in PP were observed. Furthermore, yieldlike behavior in the viscosity and a tail in the low-frequency behavior of the elastic modulus was attributed to the reaction of PP-g-MA with the nanoclay surface and not exfoliation. A fairly well-dispersed morphology was observed for concentrations as high 6.8 wt % clay when the clay was expanded and mixed with CO2. At this concentration, mechanical properties such as yield strength and modulus increased by as much as 13 and 69%, respectively, relative to the pure PP. Furthermore, the modulus of the composite samples prepared with PP-g-MA and CO2 was some 15% higher than that of samples prepared by direct melt compounding (without the use of CO2). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Crystallization behaviors and mechanical properties of poly(ethylene 2,6‐naphthalate)/multiwall carbon nanotube nanocomposites

AbstractCarbon nanotube (CNT)‐reinforced poly(ethylene 2,6‐naphthalate) (PEN) nanocomposites were prepared by direct melt blending process in a twin‐screw extruder. There is significant dependence of the crystallization and melting behavior of PEN/CNT nanocomposites on CNT content and crystallization temperature. The incorporation of CNT may favor the formation of the β‐form crystals in PEN/CNT nanocomposites, and more CNT content amplified this effect. In this PEN/CNT nanocomposite system, the CNT promoted the nucleation and the growth with higher crystallization rate of PEN/CNT nanocomposites, and simultaneously reduced the fold surface free energy and the work required in folding polymer chains in the polymer nanocomposites. In addition, the incorporation of a very small quantity of CNT significantly improved the mechanical properties of PEN/CNT nanocomposites. POLYM. ENG. SCI., 47:1715–1723, 2007. © 2007 Society of Plastics Engineers

An improved technique for exfoliating and dispersing nanoclay particles into polymer matrices using supercritical carbon dioxide

An environmentally benign process, which uses supercritical carbon dioxide (sc-CO2) as a processing aid, is developed in this work to help exfoliate and disperse nanoclay into the polymer matrices. The process relies on rapid expansion of the clay followed by direct injection into the extruder where the mixture is dispersed into the polymer melt. Results from the mechanical properties, rheological studies, and X-ray diffraction (XRD) show that this method represents a significant improvement relative to direct melt blending in single or twin-screw extruders or other methods using sc-CO2. The greatest mechanical property response was a result of directly injecting pre-mixed sc-CO2 and nanoclay into the polypropylene melt during extrusion. It was observed that for concentrations as high as 6.6wt% (limited only by present process capabilities), XRD peaks were eliminated, suggesting a high degree of exfoliation. Mechanical properties such as modulus increased by as much as 54%. The terminal region of the dynamic mechanical spectrum was similar to that of the base polymer, contrary to what is frequently reported in the literature.