Reactive extrusion processing of polypropylene/SiO2 nanocomposites by in situ synthesis of the nanofillers: Experiments and properties

The concept of a lab-scale developed in situ sol–gel batch process for fabrication of polypropylene (PP)/silica nanocomposites based on a solvent-free silica precursor polymer, a hyperbranched polyalkoxysiloxane (PAOS), has been transferred to a continuous industrially applicable extrusion process. To achieve a suitable process set-up for the continuous in situ synthesis of nanofillers in the PP melt, process parameters are varied. The influence of process parameters on precursor conversion, size and distribution of the formed silica particles and the mechanical properties of the resulting PP nanocomposites is determined. In addition, these materials are compared to conventional silica composites based on melt mixing process. It was found, that a PAOS conversion to silica particles of more than 90% could be realised using a hexadecyl-modified PAOS of 12.5% degree of modification (C₁₆(12.5%)-PAOS) at the given process set-up. Well distributed, small silica particles without any agglomeration were yield in the resulting composites in comparison to application of silica powder.     

In situ solvothermal synthesis and characterization of transparent epoxy/TiO2 nanocomposites

A solvothermal process was developed to in situ prepare epoxy (EP)/TiO₂ hybrid precursors. The chemical structure of samples was confirmed by X-ray and Fourier transformed infrared spectroscopy. Field emission scanning electron microscope micrographs of cured EP/TiO₂ hybrid composites showed that well-dispersed TiO₂ nanoparticles were successfully in situ formed in epoxy matrix through the solvothermal process. The thermogravimetic analysis, DSC, and gel content measurements showed that EP/TiO₂ hybrid precursors were fully cured with the glass transition temperature decreasing gradually. The effect of TiO₂ contents on optical and surface properties was investigated in detail. The results indicated that epoxy/TiO₂ nanocomposites exhibited excellent UV shielding effect and high visible light transparency. The contact angle of EP/TiO₂ nanocomposites, when the content of silane-coupling agent (KH560) was 5 g and the content of tetrabutyl titanate (TBT) was 3 g, can reach as high as 101°, which was 36° higher than that of pure EP, representing for the increase of hydrophobicity. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Solvent‐assisted extrusion of polypropylene/clay nanocomposites

Polypropylene (PP) nanocomposites were prepared by a melting‐compounding process with a montmorillonite (MMT) suspension. In this process, an organically modified MMT was swollen in a polar solvent and blended with molten PP in an extruder; this was followed by solvent removal. The effect of a coswelling agent was also evaluated. The nanocomposites were characterized with X‐ray diffraction, transmission electron microscopy, differential scanning calorimetry, and scanning electron microscopy. In addition, the mechanical properties of the materials were studied. The nanocomposites prepared with the clay suspension presented a remarkable increase in the impact strength with the maintenance of their flexural modulus. The mechanical properties of the nanocomposites were found to be related to the interaction between PP and the clay. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Photoactivity of Poly(lactic acid) nanocomposites modulated by TiO2 nanofillers

Photoactivity of poly(lactic acid) (PLA) nanocomposites is of great interest for rational design of products for either short‐term/single‐use or long‐term/durable applications. We prepared PLA/TiO₂ nanocomposite films through a solution mixing/film casting method. Results showed that photodegradability/photostability of PLA could be well modulated by selecting appropriate TiO₂ nanofillers. TiO₂ nanoparticles and nanowires were characterized using X‐ray diffraction, UV–Vis–NIR spectrophotometer, and scanning electron microscopy. Changes in color, weight, structure, thermal stability, and phase transitions of PLA and nanocomposite films before and after UV irradiation were evaluated to study photoactivity characteristics. Pure PLA exhibited moderate photodegradability, but the photodegradability and photostability of PLA nanocomposites (PNA) were significantly enhanced by NanoActive (NA) TiO₂ nanoparticles and A type TiO₂ nanowires, respectively. Pure PLA had a weight loss of 27% after 38 days of UV irradiation. The weight loss of photodegradable (PD) PNA (PNA = PLA with 1% NA TiO₂) reached 38%, whereas that of photostable (PS) nanocomposites (P3AW) (P3AW = PLA with 3% A type TiO₂ nanowire) was only 5%. PD PLA exhibited characteristic peaks of carboxylic acid OH stretching and C?C double bond after UV irradiation in Fourier‐transform infrared spectra, whereas spectra of PS PLA remained almost the same. Thermal decomposition temperatures, glass transition temperatures, and melting temperatures of PD PLAs decreased dramatically after UV irradiation, but no obvious changes were observed for those of PS PLAs. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40241.     

A die rotating system for moderations of extrusion load and pressure drop profiles for molten PP and wood/polypropylene composites in extrusion processes

A die‐rotating system was proposed in this work for moderations of extrusion forces and entrance pressure drop for molten polypropylene (PP) and wood/polypropylene (WPP) composites in a capillary rheometer and a single screw extruder. The effects of processing conditions and wood loading in PP were of our interests. The extrusion force and entrance pressure drop with and without the die rotating system were monitored in real‐time. This was the first time that the die‐rotating system was used for processing of highly viscous wood/polymer composite materials. It was found that the flow properties of the molten PP and WPP composites obeyed pseudoplastic non‐Newtonian behavior. The behavior was more obvious at wood contents of above 6 wt % and in the capillary rheometer. The rotation of the die could moderate the extrusion load by 60% and entrance pressure drop by 20% in the capillary rheometer, and the entrance pressure drop by 30% in the single screw extruder, especially at the conditions where the viscosities of the WPP and the extrusion rate were high. Greater fluctuations in entrance pressure drop caused by die rotation were observed in the single screw extruder. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120:1006–1016, 2011     

PVDFBaTiO3/carbon nanotubes ternary nanocomposites: Effect of nanofillers and processing

Ternary thermoplastic systems based on poly(vinylidene fluoride), PVDF, filled with barium titanate, BaTiO₃, submicrometric particles and carbon nanotubes, CNT, were prepared. Their structure and morphology were studied as a function of composition and finally correlated with thermal and mechanical properties. High energy ball milling, HEBM, under cryogenic conditions and subsequent hot pressing were used to obtain films with quite uniform dispersion of the nanofillers. The presence of BaTiO₃ particles and CNT did not modify the thermodegradation mechanism of the PVDF. However, enough amount of BaTiO₃ seemed to inhibit the volatility of the products of pyrolysis, hindering the decomposition of PVDF. The presence of CNT favored the PVDF thermodegradation probably due to improved heat transmission by an increase in the thermal conductivity. Variations in PVDF thermal transitions were more dependent of processing conditions. Improvements in the mechanical properties of PVDF were ascribed to a reinforcing effect of the fillers. This effect only happened below the fraction of percolation of CNT, pointing out that CNT reinforce through an optimum load transfer from the PVDF matrix to the nanofillers. POLYM. COMPOS., 38:227–235, 2017. © 2015 Society of Plastics Engineers     

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

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

Water-assisted extrusion as a novel processing route to prepare polypropylene/halloysite nanotube nanocomposites: Structure and properties

Naturally occurring halloysite nanotubes (HNTs) are used to prepare Polypropylene (PP)/HNTs nanocomposites using a novel “one step” water-assisted extrusion process with and without the use of a PP-graft-maleic anhydride (PP-g-MA) as compatibilizer. In order to analyze the influence of PP-g-MA and/or water injection on the HNTs dispersion and therefore on nanocomposite properties, structural analysis (SEM and TEM) is combined with rheological and thermo-mechanical experiments. The best clay dispersion is obtained when compatibilizer and water injection are combined together (synergistic effect). As a consequence, the linear viscoelastic properties and the dynamic storage modulus are dramatically enhanced for this system. A mechanism explaining the interaction between HNTs and PP-g-MA in presence of water is proposed. The thermal stability and flame retardant property are also investigated. Thermal analyses reveal two opposite effects of HNTs on the thermal behaviour of PP. A surface catalytic action of the halloysite speeds up thermal degradation of PP. However, this effect is reduced with improved HNTs dispersion, presumably via an entrapment mechanism of the decomposition products inside the lumens. Finally, cone calorimeter results show that low flammability of nanocomposites is only achieved when combining water injection and PP-g-MA. In view of these results, PP/HNTs nanocomposites prepared using this novel processing route are promising candidates for flame retardant applications.     

Preparation of high-refractive-index PMMA/TiO2 nanocomposites by one-step in situ solvothermal method

High-refractive index polymeric materials, which are transparent, have many promising applications in optical design and advanced optoelectronic fabrication. In order to improve the refractive index of polymeric materials, inorganic materials with high-refractive index, such as TiO₂, are always added into polymers. However, some of the traditional synthetic methods are complicated and hard to control. In our work, we developed a novel and simple method, a one-step in situ solvothermal method, to prepare poly(methyl methacrylate) (PMMA) and nano-TiO₂ hybrid films. Methyl methacrylate (MMA), vinyltrimethoxysilane (VTMO), titanium butoxide [Ti(OBu)₄], ethanol, hydrochloric acid, azobis-isobutyronitrile and tetrahydrofuran were added into a reaction vessel altogether and the polymerization of PMMA matrix and the formation of nano-TiO₂ composite carried out simultaneously. To improve the adhesion between PMMA and TiO₂, VTMO was used as a comonomer. The results indicate that TiO₂ nanoparticles produced by decomposition of titanium butoxide are dispersed homogeneously in the PMMA matrix. The size of TiO₂ crystals in PMMA/TiO₂ nanocomposites is about 5–6 nm. The hybrid films have a good transparency (over 80 %) in the visible region, a good thermal stability and a UV-shielding property after the incorporation of TiO₂. The refractive index of as-formed PMMA/TiO₂ nanocomposites increases up to 1.839 at 633 nm as the content of Ti(OBu)₄ is 50.00 wt%.     

Supercritical CO2‐assisted synthesis of polystyrene/clay nanocomposites via in situ intercalative polymerization

Cyclodextrins can form inclusion complexes with different molecules with the aid of their special chemical (molecular) structures. Physical and chemical properties of molecules can change after the formation of complex. This special feature enables the usage of dextrins in different industry areas. In this study, applicability of cylcodextrins in textile dyeing and washing processes was investigated. With this aim, β‐cyclodextrin was used in direct dyeing of cellulosic fabrics and in rinsing processes of direct dyed fabrics. Retarder/leveling effect of β‐cyclodextrin in dyeing process has been studied and the results were compared with that of a commercial product. In general, cyclodextrins were used in washing processes to remove the absorbed surfactants. It has been investigated whether this effect was the same for washing of dyed fabrics. Eight different direct dyes, for which the chemical structures are known, were used in dyeing and washing processes, and effect of β‐cyclodextrin on different chemical structures was investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 208–218, 2006     

Preparation,characterization, and properties of TiO2/PLA nanocomposites by in situ polymerization

In situ polymerization method was used to prepare TiO₂/polylactide (PLA) nanocomposites with different contents of TiO₂ in this work. The size of the organically modified TiO₂ particles was investigated by X‐ray diffraction (XRD) analysis. Scanning electron microscope (SEM) shows that nano‐TiO₂ particles disperse in the PLA evenly when the content of TiO₂ is low (less than 3 wt%). The differential scanning calorimeter (DSC), thermogravimetry analysis (TGA), and tensile test were used to study the thermal and mechanical properties of the composites. Results show that both the thermal and mechanical properties are markedly improved when the content of TiO₂ is 3 wt%. UV light irradiation and solution degradation experiment show that degradation of the composites is higher when the content of TiO₂ increases and due to the introduction of TiO₂ particles in the nanocomposites, the TiO₂/PLA nanocomposites exhibit remarkable bacteriostasic activity. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Mechanical properties of polypropylene/clay nanocomposites: Effect of clay content,polymer/clay compatibility,and processing conditions

In this work, polypropylene/clay nanocomposites with 0.5, 1, 3, and 5 wt % of montmorillonite (MMT) (unmodified clay) were prepared by intensive mixing at 50 rpm and 10 min of mixing. For the highest clay content (5 wt %), the initial materials or the processing conditions were changed to study their independent effect. On one hand, 10 wt % of PP‐graft‐MA (PP‐g‐MA) was incorporated or MMT was replaced by organomodified clays (C10A and C30B). On the other side, for the initial system, the speed of rotation (100 and 150 rpm) and the mixing time (5 and 15 min) were altered. In all cases, the state of the clay inside the matrix (DRX), the degree of dispersion in the micro (SEM) and nano (TEM) scales, and the rheological and mechanical properties were analyzed. It was found that the stiffness increased with clay content, whereas tensile and impact strength did not significantly change. Although intercalated structures were observed in the composites with unmodified clay, in the composites with modified clay or PP‐g‐MA, improved dispersion of clay in PP was found. The mechanical properties increased accordingly. The degree of dispersion of the filler in the matrix appeared to be unaffected by the changes in the processing conditions introduced. Finally, the elastic modulus was modeled by using an effective filler‐parameter model based on Halpin–Tsai equations, which also allowed estimating the relative degree of dispersion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electrochemical synthesis and in situ spectroelectrochemistry of conducting polymer nanocomposites. I. polyaniline/TiO2, polyaniline/ZnO,and polyaniline/TiO2+ZnO

The polyaniline (PAn), polyaniline/titanium dioxide (PAn/TiO₂), polyaniline/zinc oxide (PAn/ZnO), and a novel conducting polymer nanocomposites, polyaniline/titanium dioxide + zinc oxide (PAn/TiO₂+ZnO), were synthesized by in situ electropolymerization and potential cycling on gold electrode. The PAn and nanocomposite films were characterized by cyclic voltammetry, Fourier transform infra‐red (FTIR) spectroscopy, in situ resistivity measurements, in situ UV–Visible, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The differences between cathodic and anodic peaks of three redox couples were obtained for PAn and polymeric nanocomposite films. During cathodic and anodic scans, the shift of potential was observed for polymer nanocomposite films. The characteristic FTIR peaks of PAn were found to shift to lower wavelengthsin polymer nanocomposite films. These observed effects have been attributed to interaction of TiO₂, ZnO, and TiO₂+ZnO particles with PAn molecular chains. Significant differences from in situ resistivity of PAn and nanocomposite films were obtained. The resistance of PAn/TiO₂, PAn/ZnO, and PAn/TiO₂+ZnO films were found to be smaller than the PAn film. The in situ UV–Visible spectra for Pan and polymer nanocomposite films were studied. The results show the intermediate spectroscopic properties between PAn and polymer nanocomposite films. The morphological analyses of PAn and nanocomposite films have been investigated. The nanocomposites SEM and TEM micrographs suggest that the inorganic semiconductor particles were incorporated in organic conducting polymer, which consequently modifies the morphology of the films significantly. POLYM. COMPOS., 35:351–363, 2014. © 2013 Society of Plastics Engineers     

Evaluation of PP/EPDM nanocomposites filled with SiO2, TiO2 and ZnO nanofillers as thermoplastic elastomeric insulators

Abstract

Thermoplastic elastomer, which has important characteristics for cable insulation, was developed by melt blending of polypropylene (PP) with ethylene propylene diene monomer (EPDM) at various blend ratios together with SiO₂, TiO₂ and ZnO nanofillers at fixed loading of 2 vol.-%. The influence of EPDM content and the presence of nanofillers in the blend on burning rate, hydrophobicity and dielectric breakdown strength were investigated. Burning rate of PP/EPDM/ZnO was significantly reduced, implying that there was an improvement in fire retardancy with the addition of ZnO nanofillers in the polymer blend. Both SiO₂ and ZnO filled system showed an improvement in hydrophobicity. Furthermore, dielectric breakdown strength showed higher value in EPDM rich blends. In addition, the presence of nanofillers deteriorated the dielectric breakdown strength of PP/EPDM nanocomposites.     

In situ compatibilization of polypropylene/polystyrene blend by controlled degradation and reactive extrusion

In situ compatibilization of polypropylene (PP) and polystyrene (PS) was achieved by combinative application of tetraethyl thiuram disulfide (TETD) as degradation inhibitor and di‐tert‐butyl peroxide as degradation initiator in the process of reactive extrusion. The PP/PS blends obtained were systematically investigated by rheological measurement, scanning electron microscopy, and differential scanning calorimetry. The results indicate that peroxide‐induced degradation of PP can be effectively depressed by adding TETD, which may favor the formation of PP‐g‐PS copolymer during melt processing. The PP‐g‐PS copolymer formed may act as an in situ compatibilizer for PP/PS blends, and subsequently decreases the size of dispersed PS phase and changes both rheological and thermal properties of the blends. Based on the present experimental results, the mechanisms for the controlled degradation of PP and in situ formation of PP‐g‐PS copolymer in the PP/PS blends have been proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Reactive processing of PA6/EPDM-MA blends as modifier for application and development of high-performance polypropylene

In this work, PA6/EPDM-MA was added as an impact modifier for high-performance polypropylene (PP) production. PA6/EPDM-MA compounds were processed in an internal mixer, aiming at chemical reaction between maleic anhydride of EPDM-MA and the amine terminal groups of PA6. Afterward, PP/(PA6/EPDM-MA) blends were processed by extrusion and injection molding. Rheological properties were evaluated using torque rheometry; additionally, Fourier transform infrared spectroscopy, Molau test, impact and tensile strengths, Shore D hardness, thermal deflection temperature, X-ray diffraction, differential scanning calorimetry, thermogravimetry, water absorption, contact angle, and scanning electron microscopy tests were performed in injected specimens. PP/(PA6/EPDM-MA) with 70/(15/15)% displayed quite high increase in impact and elongation at break, with gains of 850% and 265%, compared to neat PP. There were no drastic losses in tensile strength, elastic modulus, and Shore D hardness, due to PA6 addition. A significant increase was seen in the thermal stability of PP/(PA6/EPDM-MA), corroborating the increase in structural stability seen in HDT. SEM images showed high interfacial adhesion between PP and PA6/EPDM-MA corroborating higher mechanical properties. Summing up, PA6/EPDM-MA premix acted as an efficient impact modifier for PP. Acquired data show that P6/EPDM-MA system was effective in developing high-performance PP with potential for application in the automotive and electronics industries.     

Twin‐screw extrusion compounding of polypropylene/organoclay nanocomposites modified by maleated polypropylenes

Polypropylene/organoclay nanocomposites modified with different maleic anhydride grafted polypropylene (PPgMA) compatibilizers were compounded on a twin‐screw extruder. The effectiveness of the feeding sequence and compatibilizer type toward the dispersion of organoclay into PP matrix was critically studied. The composites prepared with side feed appeared to provide better dispersion and modulus improvement over that with hopper feed. The effect of PPgMA compatibilizers, including PB3150, PB3200, PB3000, and E43, with a wide range of maleic anhydride (MA) content and molecular weight was also examined. The structure was investigated with X‐ray diffraction and transmission electron microscopy. The relative complex viscosity curves also revealed a systematic trend with the extent of exfoliation and showed promise for quantifying the hybrid structure of the nanocomposites. Mechanical properties were determined by dynamical mechanical analysis and tensile and impact tests. Maleated polypropylene with low‐melt flow index and moderate MA content enhanced clay dispersion and resulted in significant improvement in tensile modulus of the nanocomposites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 100–112, 2004     

In situ synthesis and properties of PMR PI/SiO2 nanocomposites

Phenylethynyl-terminated polymerization of monomer reactant thermosetting polyimide (PI) was synthesized, and the PI/SiO₂ nanocomposite films were prepared via in situ polymerization of monomer with the nano-SiO₂ particles. Analysis indicated that the surfaces of the nano-SiO₂ slightly react to the PI, and nano-SiO₂ was homogeneously dispersed in the PI at low filling content while agglomerate was a presence of high filling content. Thermogravimetric analysis showed that the decomposition temperatures of the PI/SiO₂ nanocomposites were increasing as the increasing of filler contents when the nano-SiO₂ content was below 9 wt %, but it showed a decreased tendency when it was above 9 wt %. Tribological studies showed that the nano-SiO₂ contributed to the significant decreasing of the friction coefficient and wear rates of the PI at dry sliding condition of low filler content, and the PI/SiO₂ nanocomposites could be promising material used as tribomaterial in dry sliding condition against GCr15 steel. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

In situ compatibilization of PEN/LCP blends by ultrasonic extrusion

In situ compatibilization of immiscible blends of PEN and thermotropic LCP was achieved by the ultrasonically‐aided extrusion process. Ultrasonically‐treated PEN underwent degradation, leading to a decrease of its viscosity. Viscosity of LCP was unaffected by ultrasonic treatment. Because of reduced viscosity ratio of PEN to LCP at high amplitude of ultrasonic treatment, larger LCP domains were observed in molding of the blends. LCP acted as a nucleating agent, promoting higher crystallinity in PEN/LCP blends. Ultrasonically‐induced copolymer formation was detected by MALDI‐TOF mass spectrometry in the blends. Ultrasonic treatment of 90/10 PEN/LCP blends improved interfacial adhesion in fibers spun at intermediate draw down ratios (DDR), improving their ductility. The lack of improvement in the mechanical properties of fibers spun at high DDR after ultrasonic treatment was attributed to the disturbance of interfacial copolymer by high elongation stresses. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Influence of screw profile and extrusion conditions on the microstructure of polypropylene/organoclay nanocomposites

Direct melt mixing in a twin screw extruder is a simple and classical technique for preparing nanocomposites by dispersing organoclay in a thermoplastic matrix. In this paper, we focus on organoclay/polypropylene nanocomposites, using maleated polypropylene as compatibilizer. The objective of the work is to characterize the influence of screw profile and processing conditions on the microstructure of the nanocomposite (intercalation and exfoliation). Different screw profiles, more or less severe in terms of mixing elements, have been investigated. For each profile, different processing conditions (feed rate, screw speed) have been tested. Samples were collected both at die exit and all along the screw profiles and analyzed (X‐ray diffraction and rheometry). Numerical simulations have been performed to quantify the thermomechanical treatment experienced by the material inside the extruder. For all profiles and operating conditions, a mixed intercalated/exfoliated structure has been observed. Exfoliation increases linearly with the ratio of screw speed to feed rate, but is more important for the less severe profile. Except at low feed rate, intercalation and exfoliation do not change a lot along the screw profile. In many cases, the final microstructure is already obtained after the melting zone of the extruder. POLYM. ENG. SCI., 47:2100–2109, 2007. © 2007 Society of Plastics Engineers