Coincorporation of nano‐silica and nano‐calcium carbonate in polypropylene

In this study, various polypropylene (PP) nanocomposites were prepared by melt blending method. The effects of different spherical nanofillers, such as 50 nm CaCO₃ and 20 nm SiO₂, on the linear viscoelastic property, crystallization behavior, morphology and mechanical property of the resulting PP nanocomposites were examined. Rheological study indicated that coincorporation of nano‐SiO₂ and nano‐CaCO₃ favored the uniform dispersion of nanoparticles in the PP matrix. Differential scanning calorimeter (DSC) and polarizing optical microscopy (POM) studies revealed that the coincorporation of SiO₂ and CaCO₃ nanoparticles could effectively improve PP crystallizability, which gave rise to a lower supercooling temperature (ΔT), a shorter crystallization half‐life (t_1/2) and a smaller spherulite size in comparison with those nanocomposites incorporating only one type of CaCO₃ or SiO₂ nanoparticles. The mechanical analysis results also showed that addition of two types of nanoparticles into PP matrix gave rise to enhanced performance than the nanocomposites containing CaCO₃ or SiO₂ individually. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of nanoparticle treatment on the crystallization behavior and mechanical properties of polypropylene/calcium carbonate nanocomposites

Effects of nanoparticle surface treatment on the crystallization behavior and mechanical properties of polypropylene (PP)/CaCO₃ nanocomposites were investigated by using differential scanning calorimetry (DSC), polarized optical microscope (POM), X‐ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The results demonstrated that the interfacial interaction formed between PP and nanoparticles significantly influenced the thermal and mechanical properties of nanocomposites. It was found that CaCO₃ nanoparticles modified by a single aluminate coupling agent (CA‐1) could improve the onset crystallization temperature more effectively than that modified by a compound surface‐treating agent (CA‐2) could. However, there is no significant difference in total rate of crystallization for the two PP/CaCO₃ nanocomposites (PPC‐1 and PPC‐2), which contained CA‐1 and CA‐2, respectively. In contrast, CA‐2 modified nanoparticles could cause smaller spherulites and induce much more β‐phase crystal in nanocomposites than that of CA‐1 modified nanoparticles. This may be explained by a synergistic effect of aluminate coupling agent and stearic acid in CA‐2, which also resulted in an improved toughness for PPC‐2. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 3480–3488, 2006     

Influences of polypropylene grafted to SiO<Subscript>2</Subscript> nanoparticles on the crystallization behavior and mechanical properties of polypropylene/SiO<Subscript>2</Subscript> nanocomposites

Influences of polypropylene (PP) grafted to SiO₂ nanoparticles (7 nm) were studied on the crystallization behavior and the mechanical properties of PP/SiO₂ nanocomposites. PP for the matrix and grafting was synthesized in order to have an identical primary structure, aiming at their co-crystallization and resulting reinforcement of filler-matrix interfaces. The grafted PP chains improved the dispersion of SiO₂, and notably accelerated nucleation in crystallization. It was plausible that the grafted chains whose one chain end was pinned to SiO₂ became nuclei of the crystallization (co-crystallization between the matrix and grafted chains), thus directly bridging between the matrix and SiO₂ nanoparticles. The Young’s modulus and tensile strength were most improved by the grafted PP chains at low filler contents such as 2.3 wt%, whose origin was attributed to effective load transfer to SiO₂ through the co-crystallization-mediated bridging.     

Combined effect of organic phosphate sodium and nanoclay on the mechanical properties and crystallization behavior of isotactic polypropylene

Combined effect of α‐nucleating agent (NA) sodium 2,2′‐methylene‐bis(4,6‐di‐tert‐butylphenyl) phosphate (NA11) and nanoclay (NC) on the mechanical properties and crystallization behavior of isotactic polypropylene (iPP) was investigated by mechanical testing, wide‐angle X‐ray scattering (WAXD), differential scanning calorimetry (DSC), polarized optical microscopy (POM), and scanning electron microscopy (SEM). The mechanical testing results indicated that the separate addition of NA11 and NC only increased the stiffness of iPP while the combined addition of NA11, NC, and maleic anhydride grafted polypropylene (PP‐g‐MA) simultaneously improved stiffness and toughness of iPP. Compared to pure iPP, the tensile strength, the flexural modulus, and impact strength of iPP composites increased 9.7, 38.6, and 42.9%, respectively. The result indicated good synergistic effects of NC, NA11, and PP‐g‐MA in improving iPP mechanical properties. WAXD patterns revealed NA11, and NC only induced the α‐crystals of iPP. SEM micrograph showed that the PP‐g‐MA could effectively improve the dispersing of NC in iPP. Finally, the nonisothermal crystallization kinetics of neat iPP and PP nanocomposites was described by Caze method. The result indicated that the addition of NA overcame the shortcoming of low crystallization rate of NC nanocomposites and maintained the excellent mechanical properties, which is another highlight of the combined addition of NAs and nanoclay. Meanwhile, the result showed that nuclei formation and spherulite growth of iPP were affected by the presence of NA and nanoclay. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of polyoxyethylene nonylphenol on dynamic mechanical properties and crystallization of polypropylene

Polypropylene (PP) was blended with polyoxyethylene nonylphenol (PN) in a twin-screw extruder and injection moulded. The dynamic mechanical properties of PP/PN blends were characterized by dynamic mechanical analyser (DMA). The glass transition temperature (T_g) of PP showed a slight decrease with incorporation of PN. Differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and polarized optical microscopy (POM) were employed to investigate the effects of PN on crystallization of PP. In a study of nonisothermal crystallization of PP and PP/PN blends, crystallization parameter analysis showed the addition of PN reduced the peak temperature of crystallization. β-form crystals of PP coexisted with α-form crystals in PP/PN blends, and oriented on the surface layer of injection moulded bar as revealed by WAXD. The degree of orientation was determined using Hermans orientation function. The thermal stability of β-form crystals was evaluated using high temperature WAXD and POM.     

Improvement of polyamide 1010 with silica nanospheres via in situ melt polycondensation

Polyamide 1010 (PA1010) had been prepared by in situ melt polycondensation in presence of silica nanospheres with amine groups on the surfaces (SiO₂ NH₂). Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), and thermal gravimetric analysis (TGA) measurements demonstrated that the nanosphere surface was grafted with PA1010 chains. Wide angle X‐ray diffraction (WAXD) and differential scanning calorimetry (DSC) measurements showed that the PA1010/SiO₂ NH₂ nanocomposites had a lower degree of crystallinity (χ_c) in comparison with PA1010 and PA1010/SiO₂ nanocomposites. Dynamic mechanical analysis (DMA) indicated that SiO₂ NH₂ nanospheres improved glass transition temperature (T_g), tensile strength and storage modulus of PA1010 since SiO₂–NH₂ nanospheres limited the mobility of PA1010 chains. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Influence of incorporation sequence of silica nanoparticles on morphology,crystallization behavior,mechanical properties,and thermal resistance of melt blended thermoplastic natural rubber

Thermoplastic natural rubber nanocomposites based on epoxidized natural rubber (ENR) and polypropylene blends at a fixed blend ratio of 50/50 wt% reinforced with small amount (2.5 wt%) of nanosilica (SiO₂) were prepared by melt‐mixing through three different incorporation sequences in an internal mixer. The effects of incorporation techniques on morphology, crystallization behavior, mechanical properties, dynamic, rheological characteristics, and thermal resistance of thermoplastic natural rubber (TPNR) nanocomposites were investigated. It was found that the dispersion of nanosilica in TPNRs was significantly dependent on the incorporation sequence. In the case where SiO₂ was premixed in ENR before blending with polypropylene (PP), the final morphology showed the good dispersion of SiO₂ in ENR phase, while the SiO₂ particles were localized near the PP interface when SiO₂ was premixed the in PP first. Whereas, when the three components were simultaneously mixed, the SiO₂ particles were mainly dispersed in the PP phase. It was also found that the improvements of Young's modulus, tensile strength, damping behavior, and thermal stability of TPNR nanocomposites were more pronounced when the SiO₂ particles localized in ENR phase. By contrast, the presence of SiO₂ particles in PP domain either near the interface or inside the PP phase affected the reduction in crystallinity of PP phase and showed a negative effect on mechanical properties due to the poor interface interaction between PP and SiO₂ particles. POLYM. COMPOS., 33:1911–1920, 2012. © 2012 Society of Plastics Engineers     

Effects of particle type on thermal and mechanical properties of polyoxymethylene nanocomposites

The effects of particle size of titanium dioxide (TiO₂) on mechanical, thermal, and morphological properties of pure polyoxymethylene (POM) and POM/TiO₂ nanocomposites were investigated and compared with the results for nanoparticle ZnO in the same matrix, reported in a previous paper. POM/TiO₂ nanocomposites with varying concentration of TiO₂ were prepared by the melt mixing technique in a twin screw extruder, the same method that used for blending the homogeneous ZnO nanocomposites. The dispersion of TiO₂ particles in POM nanocomposites was studied by scanning electron microscopy (SEM). The agglomeration, as observed by the mechanical properties of TiO₂ particles in the polymer matrix, increased with increasing TiO₂ content, a result not found for ZnO even at lower particle sizes. Increasing the filler content of POM/TD32.4 and POM/TD130 (130 nm) nanocomposites resulted in a decrease in tensile strength. The Young modulus, stress at break and impact strength of TiO₂ nanocomposite did not improve with increasing filler contents, in opposition to the better agglomeration conditions of ZnO nanocomposite even at lower particle sizes. Because of agglomeration, the POM/TD32.4 nanocomposites had lower mechanical properties and lower degradation temperature than the POM/TD130 ones. The sizes of nanoparticles determined the agglomeration, but however, the agglomeration also depended on the type of nanoparticles, even when using the same matrix (POM) and the same mixing method. TiO₂ nanoparticles were more difficult to mix and were more agglomerated in the POM matrix as compared to ZnO nanoparticles, regardless of the size of the nanoparticles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Structure and properties of polypropylene composites filled with magnesium hydroxide

Silane and silicone oil modified superfine magnesium hydroxide (MH) was filled into polypropylene (PP) as a flame retardant. The PP and flame‐retarded PP composites were studied for their mechanical properties and rheological behaviors by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), limiting oxygen index (LOI), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The results showed that the addition of MH improved flame retardancy of PP/MH composites, but seriously deteriorated mechanical properties of the composites. Surface treatment of MH could significantly improve tensile and impact strength of PP/MH composite because of its enhanced interfacial adhesion between MH and PP matrix. DSC results showed that MH had heterogeneous nucleation effect on PP. Surface treatment of MH weakened its heterogeneous nucleation effect. POM results showed that the dispersion of MH particles played an important role in the crystalline morphology and spherulite size of PP crystals. TGA indicated that MH greatly enhanced the thermal stability of PP. The introduction of treatment agent further improved the thermal oxidative stability of the composite. According to LOI, silane‐treated MH greatly enhanced flame retardancy of PP/MH composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4943–4951, 2006     

Study on Mechanical Properties and Crystallization Behavior of Polypropylene and Its Blends Modified by β Crystalline Form Nucleating Agent

The influence of β crystalline form nucleating agent (β nucleator) on the mechanical properties of homo-polymerized polypropylene (PPH), random-copolymerized polypropylene (PPR), block-copolymerized polypropylene (PPB), and PPH/PPR/PPB blends was studied. Polarized optical microscopy (POM), differential scanning calorimetry (DSC), and wide angle X-ray diffraction (WAXD) were used to characterize the crystalline morphology and behavior. The results indicated that α crystalline form of polypropylene (PP) had transformed to β crystalline form by adding 0.5% β nucleator; in the meantime, the toughness of PP and its blends was enhanced. That is, 0.5% β nucleator helped to improve the notched impact strength of PPH, PPR, and PPH/PPR/PPB blends by 130%, 40%, and 40%, respectively, without losing the tensile strength and flexural strength.     

Preparation and characterization of fluorinated polypropylene by reactive extrusion with fluorinated acrylate

The fluorinated polypropylene (PP) was prepared by reactive extrusion, in which PP was grafted with fluorinated acrylate, acrylic acid 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluoro-nonyl ester (HFNAE). The Fourier transformed spectroscopy results confirmed the graft polymerization on PP backbone by the reactive extrusion. The surface tension of these polymer materials and the influence of HFNAE on the crystalline behavior had been investigated with static contact angles apparatus, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and the polarized optical microscope (POM). The surface tension of fluorinated PP was found to be less than that of the untreated polypropylene. The results showed that the fluorinated acrylate (HFNAE) might induce β form crystals when being grafted into PP from the result of WAXD and DSC. The spherule configuration difference between PP and fluorinated PP could be observed with POM photos. The result from the isothermal crystallization kinetic analyses indicated that the speed of the forming nuclear for the regular PP was smaller than that of the fluorinated PP. In addition, the addition HFNAE improved impact strength and thermal stability of PP, but the tensile tension decreased slightly.     

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     

NONISOTHERMAL CRYSTALLIZATION KINETICS AND MECHANICAL PROPERTIES OF PP/NANO-SiO2 COMPOSITES

The nonisothermal crystallization kinetics of polypropylene (PP)/nano-SiO₂ composites was studied by means of differential scanning calorimetry (DSC). The modified Avrami theories by Jeziorny, Ozawa, and Mo were used to analyze the data of DSC. The results showed that both the Jeziorny and Mo methods could describe this system very well, but the Ozawa analysis failed. The activation energy was evaluated by the Kissinger method. It was found that the crystallization activation energy of PP was higher than that of PP/nano-SiO₂ composites. The determined results of mechanical properties showed that the addition of nano-SiO₂ increased the mechanical properties of the PP. Micrographs of Polarized optical micrograph (POM) further demonstrated that nano-SiO₂ could toughen the PP.     

Polypropylene-grafted nanoparticles as a promising strategy for boosting physical properties of polypropylene-based nanocomposites

SiO₂ nanoparticles grafted to terminally hydroxylated polypropylene (PP-g-SiO₂) with different molecular weights were melt mixed with PP to prepare a series of PP/PP-g-SiO₂ nanocomposites. PP/PP-g-SiO₂ offered several advantages over pristine PP and PP/unmodified SiO₂ such as highly uniform dispersion up to 10 wt.-%, +200–400% faster crystallization and +30% increments for both the Young's modulus and the tensile strength without largely sacrificing the melt viscosity of PP. We concluded that grafted chains act as crystallization nuclei and co-crystallize with matrix chains to make PP-g-SiO₂ nanoparticles as a physical cross-linker between lamellae, while the linkage disappears in melt and grafted chains minimize the cohesive attraction between nanoparticles.     

Polypropylene/Organoclay Nanocomposites: Effects of Clay Content on Properties

The effects of clays as nanoscale fillers have been rarely addressed. Influence of the amount of organoclay (ranging between 1 and 10 wt.%) on the nanocomposites structure, i.e., intercalated or exfoliated, and on the enhancement of mechanical, rheological and morphological properties of polypropylene (PP) nanocomposites was studied in this work. The fundamental material characterization was conducted using XRD, SEM, TEM, DSC, POM, DMTA as well as RMS. Overall mechanical properties determined by tensile tests showed improvements. DSC and POM results demonstrated decrease of nanocomposites crystallinity. XRD and TEM Showed intercalate/exfoliate structures in the resultant nanocomposites.     

Polyoxymethylene‐homopolymer/hydroxyapatite nanocomposites for biomedical applications

In this article, new polyoxymethylene (POM)/hydroxyapatite (HAp) nanocomposites for bone long‐term implants have been obtained and characterized by using FTIR, WAXD, SEM, TG, DSC, tensile tests, and in vitro evaluation. Characteristic bands both for extended chain crystals (ECC) and folded chain crystals (FCC) were observed in FTIR profiles for both pure POM and POM in POM/HAp nanocomposites. From WAXD analysis it has been found that the addition of HAp does not change the hexagonal system of POM in POM/HAp nanocomposites. Moreover, degree of crystallinity of POM increases with an increase of HAp content up to 1.0% and next decreases with an increase HAp content. It indicates that HAp nanoparticles up to 1.0% content act as effective nucleating sites. Mechanical tests revealed that Young's modulus increases, whereby, elongation at break and tensile strength decrease with increasing hydroxyapatite concentration. Results of in vitro investigations show that an increase of HAp content in POM nanocomposites facilitates formation of apatite layer on the sample surface and improves in vitro stability POM/HAp nanocomposites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of Nano CaCO<Subscript>3</Subscript> on thermal properties of Styrene Butadiene Rubber (SBR)

Styrene butadiene rubber (SBR) as matrix was reinforced separately with 9, 15 and 21 nm sizes of CaCO₃, which were synthesized by matrix mediated growth technique. The mixing and compounding was done on two-roll mill and sheets were prepared in compression molding machine. The effect of nature and loading of nano CaCO₃ on these rubber nanocomposites was investigated thoroughly by different characterizations such as DSC, TGA, XRD, and mechanical properties. An appreciable increase in glass transition temperature has been observed from DSC study. 9 nm sizes of CaCO₃/SBR composites show more increment in Tg as compared to pristine SBR as well as different sizes of CaCO₃ filled SBR. This increment in Tg is due to restricted mobility of nano CaCO₃ filled SBR nanocomposites. XRD study of nanocomposites showed that nano CaCO₃ dispersed uniformly throughout the matrix because of the small peak at lower 2θ. This uniform dispersion of nano CaCO₃ contributes towards the higher mechanical properties of rubber composites. From TGA study, it was observed that as the size of CaCO₃ reduces the thermal stability increases as compared to pristine SBR. The other results of these rubber nanocomposites were compared with commercial CaCO₃ filled SBR. Partly this research paper has been presented in International conference on ‘RubberChem 2006, Dec 5–6, 2006, Munich, Germany.     

Nanocomposites of polypropylene/titanate nanotubes: morphology,nucleation effects of nanoparticles and properties

High-quality titanate nanotubes (TiNT) were mixed with modified polypropylene (PP*) by a batch melt-mixing procedure. To improve compatibility between the nanofiller and the matrix, polypropylene (PP) was modified by electron beam irradiation. Effects of TiNT nanoparticles on crystallization, mechanical, thermal and rheological properties of the modified polypropylene were studied and compared with the analogous systems filled with commercial micro- (mTiO₂) and nano- (nTiO₂) titanium dioxide particles. Nucleation effects of the TiO₂-based fillers on PP* crystallization were investigated in detail. The microstructure of the PP*/TiNT nanocomposites shows well-dispersed TiNT sparse aggregates (clouds), penetrated by the polymer. A large-scale structure in the nanocomposite melts confirmed also rheology. In comparison to the matrix characteristics, the stiffness and microhardness of the TiNT nanocomposites increase by 27 and 33 %, respectively. The enhancement in mechanical properties demonstrates that the quality titanate nanotubes can be used as an efficient filler in non-polar polymers using the polymers modified by irradiation. In the case of the nanocomposites containing nTiO₂-anatase particles, the increase in these mechanical characteristics is lower. The investigated changes in the rate of crystallization indicate a marked nucleation effect of the nanotubes. The crystallization kinetics data, processed by the Avrami equation, suggest 3-dimensional crystal growth in the polypropylene matrix. The observed improvement in mechanical properties of the TiNT nanocomposites is induced not only by the nanofiller reinforcement but also by the changes of supermolecular structure of the polymer matrix due to nucleated crystallization.     

Preparation and characterization of PLLA–ESO/surface-grafted silica nanocomposites

Various amounts of surface-grafted silica (g-SiO₂) and un-grafted (SiO₂) nanoparticles were solution blended with a copolymer of l-lactide and epoxidized soybean oil (PLLA–ESO) or PLLA. Chemical reaction between the low molecular weight (LMW) PLLA and surface of silica nanoparticles is confirmed by FTIR and TGA analyses. The amount of grafted LMW PLLA investigated by thermal gravimetric analysis (TGA) was about 14.9%–28.2% in weight. g-SiO₂ nanoparticles can be easily dispersed into PLLA–ESO matrix to form a uniform PLLA–ESO/g-SiO₂ composite. Thermal properties of PLLA–ESO/g-SiO₂ and PLLA/g-SiO₂ nanocomposites were subsequently investigated by the differential scanning calorimeter measurements (DSC). DSC analyses indicated that g-SiO₂ nanoparticles can serve as a nucleating agent for the crystallization of PLLA–ESO in the composites, while the melting temperature (T _m) and the glass transition temperature (T _g) of PLLA–ESO/g-SiO₂ nanocomposites seemed to be independent of loading of g-SiO₂ particles. The DSC curves of PLLA/g-SiO₂ nanocomposite obviously showed double melting peaks, while that of PLLA–ESO/g-SiO₂ nanocomposites only a single melting peak. PLLA–ESO/g-SiO₂ composites exhibited a higher tensile strength and elongation than that of PLLA–ESO/SiO₂ composites.     

Effects of La3+‐containing additive on crystalline characteristics of isotactic polypropylene

The influence of a mixed additive of lanthanum stearate and stearic acid on the crystalline characteristics of isotactic polypropylene (iPP) has been investigated. The results of the wide‐angle X‐ray diffraction (WAXD) measurements and the melting behaviour examination by differential scanning calorimetry (DSC) show that the additive might induce a high proportion of β‐form and act as a β‐form nucleating agent. The relative content of β‐form estimated by WAXD is 33.1% in a PP containing 2.5% (by weight) of the additive. Isothermal crystallization at 130 °C, examined by DSC, reveals that the additive considerably accelerates the overall rate of crystallization: the half crystallization period t_1/2, decreases from 11.7 min for pure PP to 7.3 min for PP containing 2.5% of the additive. However, the additive has no obvious influence on the nucleation mechanism and crystal growth mode. Polarized light microscopy (POM) examinations indicate that the addition of the additive to PP causes spherulites to become much finer. © 2003 Society of Chemical Industry