Preparation and characterization of polypropylene/silica nanocomposites by gamma irradiation via ultrafine blend

Polypropylene/silica nanocomposites were prepared by gamma irradiation via ultrafine blend so that the silica at 3% loading level can be well dispersed to polymeric materials for improving their mechanical performance. First, ultrafine blend processing in the melt state is an effective method for improving physical dispersion of nanosilica. Then irradiation technique generates firm and impervious joint between polypropylene and silica, due to the adding of the compatibilizer, maleic anhydride grafted polypropylene. The reaction of maleic anhydride groups with the hydroxyl groups on the surface of nanosilica was characterized by Fourier Transform Infrared Spectra (FTIR). Scanning electronic microscopy (SEM), X-ray diffraction analysis (XRD), differential scanning calorimeter (DSC) and polarized optical microscope (POM) were introduced to characterize the polypropylene/silica nanocomposites. Also the mechanical properties of the nanocomposites were evaluated by tensile strength, young’s modulus and elongation at break, which showed good enhancement due to well dispersed silica and improving interface combination.     

Evaluation of polypropylene grafted with maleic anhydride and styrene as a compatibilizer for polypropylene/clay nanocomposites

Among modified Poly(propylene)s (PPs) grafted with polar monomers, PP grafted with maleic anhydride (PP-g-MAH) is known to be the most efficient compatibilizer for PP/clay nanocomposites, since it provides well-dispersed nanostructures and yields optimal physical properties of the nanocomposites. One drawback of this material, however, is that it becomes brittle and its viscosity decreases drastically, leading to nanocomposites with low toughness as the graft degree of MAH increases. Therefore, there is a limitation to increasing both stiffness and toughness of PP/clay nanocomposites with PP-g-MAH. In this study, we investigated the performance of a PP grafted with maleic anhydride and styrene (PP-g-MAH-St) as compatibilizers in PP/clay nanocomposites. It was found that the incorporation of styrene as a comonomer prevents molecular weight reduction of the PP main chain upon high loading of a radical initiator for high graft degree of MAH. The compatibilizers (PP-g-MAH-St) thus obtained show good compatibilizing performance in PP/clay nanocomposites. The PP/clay nanocomposites compatibilized by PP-g-MAH-St show both high stiffness and toughness, which is accomplished by using a compatibilizer of higher viscosity compared with PP-g-MAH.     

Mechanical and Morphological Properties of Polypropylene and Regenerated Tire-Rubber Blends

Mechanical properties and morphology of blends prepared from polypropylene (PP) and 5–20 wt% of regenerated tire-rubber (RgR) were studied. The samples were prepared in a twin-screw extruder. The addition of maleic anhydride-functionalized polypropylene (PP-g-MAH) was also investigated. Tensile and flexural moduli, tensile strength at break, elongation at break and Izod impact resistance at 23°C were increased by the addition of 15 wt% of regenerated rubber and 5 wt% of PP-g-MAH. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) analyses showed some interaction between PP and RgR and considerable modification of the compatibilized mixture morphology. The fracture surface of the blend with PP-g-MAH showed a better interaction between the PP matrix and the regenerated rubber domains, for all blends. Well-dispersed particles of the rubber in the polypropylene matrix were observed. DSC showed that PP crystallizes on cooling at lower temperatures as the RgR content increases. The decrease in crystallization temperature is more evident for blends with 5 wt% PP-g-MAH.     

Study on compatibilization of polypropylene-liquid crystalline polymer blends

The mechanical properties, melt rheology, and morphology of binary blends comprised of two polypropylene (PP) grades and two liquid crystalline polymers (LCP) have been studied. Compatibilization with polypropylene grafted with maleic anhydride (PP-g-MAH) has been attempted. A moderate increase in the tensile moduli and no enhancements in tensile strength have been revealed. Those findings have been attributed to the morphology of the blends, which is predominantly of the disperse mode. LCP fibers responsible for mechanical reinforcement were only exceptionally evidenced. Discussion of PP-LCP interfacial characteristics with respect to mechanical properties-morphology interrelations allowed evaluation of the compatibilizing efficiency of PP-g-MAH. Factors important for successful reinforcement of PP with LCP have been specified. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 969–980, 1997     

Compatibilization of PP/elastomer/microsilica composites with functionalized polyolefins: Effect on microstructure and mechanical properties

The morphology and mechanical properties of polypropylene/elastomer/silica composites were investigated with the aim of improving stiffness and impact resistance. Two different types of silica were tested: Precipitated silica and polymer grade microsilica (silica fume). The composites were compatibilized with commercial polypropylene and polyethylene containing maleic anhydride functionality as a means of controlling their microstructure and ultimately their mechanical properties. Comparisons were made with surface coated silica and hydroxyl-functionalized copolymers prepared with metallocene catalysts. The effect of adding the polymeric compatibilizers was assessed by morphology studies, thermal analysis and mechanical testing. Significant improvements in impact strength were obtained by tailoring the microstructure of polypropylene/elastomer/microsilica composites. With introduction of PP-g-MAH as compatibilizer, stiffness was enhanced simultaneously with impact strength. DSC curves of crystallization provided evidence to support the formation of different microstructures.     

Dynamic rheology and morphology of HDPE‐fumed silica composites: Effect of interface modification

In the present study, high density polyethylene (HDPE)‐based composites containing different amounts of fumed silica (FS) were prepared by melt compounding in a corotating twin screw extruder. Polyethylene‐g‐maleic anhydride copolymer (PE‐g‐MA) containing 1 wt% maleic anhydride was used for interface modification between filler and polymer. The interaction between the surface hydroxyl groups of fumed silica nanoparticles with maleic anhydride groups of PE‐g‐MA led to a finer dispersion of the filler in the HDPE matrix. The terminal complex viscosity and terminal storage modulus were highest at 1 wt% filler loading due to widely spread network formation by FS nanoparticles. This filler network plausibly got disturbed at higher filler content and/or interface modification which was reflected in their stress relaxation behavior also. The dynamic rheological behavior of the composites was explained in terms of morphological observations. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Effect of blend ratio on bulk properties and matrix-fibril morphology of polypropylene/nylon 6 polyblend fibers

Ternary blends of polypropylene (PP), nylon 6 (N6) and polypropylene grafted with maleic anhydride (PP/N6/PP-g-MAH) as compatibilizer with up to 50 wt% of N6 were investigated. PP-g-MAH content was varied from 2.5 to 10%. Blends of the two polymers PP/N6 (80/20) without the compatibilizer were also prepared using an internal batch mixer and studied. The ternary blends showed different rheological properties at low and high shear rates. The difference depended on the amount of N6 dispersed phase. Co-continuous morphology was observed for the blend containing 50% N6. This blend also exhibited higher viscosity at low shear rate and lower viscosity at high shear rates than the value calculated by the simple rule of mixture. At higher shear rates, viscosity was lower than that given by the rule of mixture for all blend ratios. An increase in viscosity was observed in the 80/20 PP/N6 blend after the concentration of the interfacial agent (PP-g-MAH) was increased. Polyblends containing up to 30% N6 could be successfully melt spun into fibers. DSC results showed that dispersed and matrix phases in the fiber maintained crystallinity comparable to or better than the corresponding values found in the neat fibers. The dispersed phase was found to contain fibrils. By using SEM and LSCM analyses we were able to show that the N6 droplets coalesced during melt spinning which led to the development of fibrillar morphology.     

Exfoliation and dispersion enhancement in polypropylene nanocomposites by in‐situ melt phase ultrasonication

A novel process using ultrasonics to enhance the exfoliation and dispersion of clay platelets in polypropylene‐based nanocomposites has been proposed and investigated. The materials studied were isotactic polypropylene of various molecular weights reinforced with organophilic montmorillonite clay (nanoclay) at 4–6 wt% loadings. X‐ray diffraction (XRD) and rheological measurements, on a model system of nanoclay in mineral oil, were first used to determine ultrasonic energy requirements. The effectiveness of the proposed ultrasonic processing technique on polypropylene nanocomposites was evaluated by XRD and transmission electron microscopy (TEM). The effects of added maleic anhydride–grafted polypropylene compatibilizer, polypropylene molecular weight, and pretreatment of the nanoclays on the nanocomposite exfoliation were also investigated. Results indicate that ultrasonic processing of polymer nanocomposites in the melt state is an effective method for improving exfoliation and dispersion of nanoclays. Issues regarding molecular weight degradation, optimization, mechanical properties, and continuous processing are beyond the scope of the present study and are currently being investigated in our laboratory. Polym. Eng. Sci. 44:1773–1782, 2004. © 2004 Society of Plastics Engineers.     

Structure and properties of polypropylene-based nanocomposites: Effect of PP-g-MA to organoclay ratio

The structure-property relationships of polypropylene (PP)-based nanocomposites prepared by melt processing have been investigated with a main focus on the ratio of polypropylene grafted with maleic anhydride (PP-g-MA) to organoclay. The morphological observations by transmission electron microscopy and X-ray diffraction are presented in conjunction with the mechanical, rheological and thermal expansion properties of these nanocomposites. Detailed morphological studies and subsequent quantitative particle analyses for the dispersed clay phase reveal that the aspect ratio of clay particles decreases as the amount of clay increases, and it increases as the amount of PP-g-MA increases. The rheological properties suggest that the extent of a percolation network can be enhanced by increasing the number of organoclay particles at a fixed ratio of PP-g-MA to organoclay and by increasing the degree of exfoliation at fixed clay content. However, mechanical and thermal expansion behaviors do not improve correspondingly in all cases because of the reduction of matrix properties by PP-g-MA. The reduction of the modulus and the increase in the expansion of the polymer matrix caused by the presence of PP-g-MA are compared to the prediction of the Chow model. Clearly, the amount of PP-g-MA added along with its lower crystallinity are important factors affecting the mechanical and thermal expansion properties of PP-based nanocomposites.     

The Effect of Spray-Freeze Drying of Montmorillonite on the Morphology,Dispersion, and Crystallization in Polypropylene Nanocomposites

The spray-freeze drying (SFD) technique was applied to sonicated aqueous suspensions of spray-dried montmorillonite clay (MMT) to produce highly porous agglomerates (SFD-MMT). Both MMT (used as a reference) and SFD-MMT were subsequently incorporated in polypropylene (PP) via melt compounding to produce 2 wt % nanocomposites with and without maleic anhydride grafted polypropylene (PP-g-MA). Polypropylene nanocomposites containing SFD-MMT exhibited thinner silicate flake layers compared to large agglomerates in PP/MMT nanocomposites. SFD-MMT particles became even more finer in the presence of PP-g-MA (i.e., in PP/PP-g-MA /SFD-MMT) where it hindered PP crystallization instead of serving as nucleation sites for the PP crystallization during rapid cooling. SFD-MMT improved the thermal stability of PP/PP-g-MA by 30°C compared to only 5–8°C for MMT/nanocomposites. MMT acts as a heterogeneous nucleating agent in the nucleation-controlled PP nanocomposites, but the hindrance effect was observed for the PP/PP-g-MA with SFD-MMT. PP/PP-g-MA/SFD-MMT exhibited twice the edge surface energy as compared to PP/PP-g-MA/MMT. The incorporation of both types of MMT raised the tensile moduli of PP and PP/PP-g-MA, with no improvement in their tensile strength and a decrease in the elongation at break. The PP/PP-g-MA/SFD-MMT showed brittle failure. POLYM. ENG. SCI., 60:168–179, 2020. © 2019 Society of Plastics Engineers     

Novel strategy for ternary polymer blend compatibilization

A novel strategy for compatibilization of ternary polymer blends was described. PP (polyolefins)/PA6 (engineering plastics)/PS (styrene polymers) was selected as a model ternary blend system, and the compatibilization effect was investigated by means of SEM, rheometer, dynamic mechanical thermal analysis and mechanical testing. The results indicated that, as a ternary polymer blend compatibilizer, styrene and maleic anhydride dual monomers melt grafted polypropylene [PP-g-(MAH-co-St)] showed more effective compatibilization in the PP/PA6/PS ternary blend system than PP-g-MAH, PP-g-St and their mixture. The good compatibilizing effect of PP-g-(MAH-co-St) can be explained by two mechanisms. One is the in situ formation of [PP-g-(MAH-co-St)]-g-PA6 copolymer at the PP/PA6 interface, and the other is that it also contains styrene blocks, resulting in chemical affinity with PS and PP homopolymers.     

Morphological,Thermal and Mechanical Properties of Polypropylene and Vermiculite Blends

Morphological, thermal and mechanical properties of blends prepared from polypropylene (PP) and 1, 3 and 5 wt% of vermiculite (VMT) were studied. The samples were prepared in a twin-screw extruder. The addition of maleic anhydride-functionalized polypropylene (PP-g-MAH) was also investigated. The blend morphologies were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The thermal properties of the composites were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The DSC results showed that PP crystallizes on cooling at higher temperatures as VMT content increases. The increase in crystallization temperature was most evident for blends with 5 wt% VMT. The TGA results showed that the use of VMT particles to fill polypropylene increased the thermal stability of the composite. The mechanical properties, tensile modulus and tensile strength at yield point of the PP improved by the presence of VMT.     

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     

In situ chlorinating-graft copolymerization on isotactic polypropylene in gas–solid phase

A novel method in situ chlorinating-graft copolymerization (ISCGC) of grafting maleic anhydride (MAH) on isotactic polypropylene (iPP) in gas–solid phase was investigated in this paper. Chlorine (Cl₂) was used as initiator, chlorinating agent and termination agent at the same time during the reaction. The iPP was chlorinated as well as grafted with MAH in the reaction process. The product with chlorine and MAH in the same molecule was named as PP-cg-MAH. Existence of PP-cg-MAH was identified by Fourier transform infrared. Thermal behavior and crystallinity of PP-cg-MAH were analyzed by differential scanning calorimetry, X-ray diffraction and polarizing microscope. Influencing factors for the value of graft degree were also discussed. Compared with conventional peroxide initiated graft method, ISCGC revealed higher MAH graft efficiency (33%), and particularly alleviated degradation of iPP. iPP could be grafted successfully and without changing physical properties dramatically through this method.     

The anhydride content of some commercial PP-g-MA: FTIR and titration

A set of anhydride-grafted polypropylenes was collected from various companies. They were studied in light of our recent results on polypropylene melt grafted with maleic an-hydride.¹ This work confirmed that an important decrease of the anhydride content is recorded on heating or washing, due to the elimination of free, ungrafted products, re-spectively, by sublimation of maleic anhydride and by polymaleic anhydride solubilization. The deconvolution of the infrared spectra of washed anhydride-grafted polypropylenes (PP-g-MA) revealed two types of grafted anhydride: succinic anhydride form and polymaleic anhydride form. All in all, four forms of anhydride functions were detected: two grafted and two free, each being either on monomeric or polymeric forms. Nevertheless, one PP-g-MA (Hercoprime) can be distinguished by its very high grafting level. This polymer is therefore discussed in more detail. Finally, all the present results are discussed with regard to the principal applications of the PP-g-MA as a blend compatiblizer or as an adhesion promoter. © 1996 John Wiley & Sons, Inc.     

Synthesis and properties of polyolefin graft copolymers by a grafting “onto” reactive process

The synthesis of graft copolymers by the grafting “onto” process in the molten state was described. Functional oligomers obtained by telomerization or by ATRP were reacted onto maleic anhydride grafted polypropylene (PP-g-MAH) and poly(ethylene-ter-maleic anhydride-ter-methyl acrylate) (P(E-ter-MAH-ter-MeA)) to obtain PP-g-PMMA and P(E-ter-MAH-ter-MeA)-g-PMMA graft copolymers, respectively. The grafting of different mono-functional oligomers bearing hydroxyl, aliphatic amine or aromatic amine functions was investigated at 180 °C and at 200 °C. The grafting efficiency was very low in the case of hydroxyl-terminated PMMA, while the amine-terminated PMMA led to high yields. In the last part, PP-g-PMMA and P(E-ter-MAH-ter-MeA)-g-PMMA graft copolymers were synthesized by the reaction of aliphatic amine functional PMMA oligomers onto PP-g-MAH and P(E-ter-MAH-ter-MeA), respectively. The influence of the molecular weight of PMMA oligomers was investigated and showed that he grafting efficiency slightly decreases with the increasing molecular weight. However, this process allows the synthesis of PP-g-PMMA graft copolymers containing 6-45 wt% of PMMA side chains. The microstructure of the nanostructured PP-g-PMMA and P(E-ter-MAH-ter-MeA)-g-PMMA graft copolymers was investigated by TEM and SEM. This was established that the addition of PP-g-PMMA in PP/PMMA binary blends allows to control their morphologies and stabilities.     

Relaxation behavior of polymer blends with complex morphologies: Palierne emulsion model for uncompatibilized and compatibilized PP/PA6 blends

This paper deals with the dynamic rheological behavior of polypropylene/polyamide6 (PP/PA6) uncompatibilized blends and those compatibilized with a maleic anhydride grafted PP (PP/PP-g-MAH/PA6). The terminal relaxation times of the blends predicted by the Palierne emulsion model were compared with those obtained from experimental relaxation time spectra. The Palierne model succeeded well in describing PP/PA6 uncompatibilized blends with relatively low dispersed phase contents (10 wt%) and failed doing so for those of which the dispersed contents were high (30 wt%). It also failed for the compatibilized ones, irrespective of the dispersed phase content (10 or 30 wt%) and whether or not interface relaxation was taken into consideration. In the case of the uncompatibilized blend with high dispersed-phase content, interconnections among inclusions of the dispersed phase were responsible for the failure of the Palierne model. As for the compatiblized blends, in addition to particle interconnections, the existence of emulsion-in-emulsion (EE) structures was another factor responsible for the failure of Palierne model. A methodology was developed to use Palierne emulsion model upon taking into account the effects of the EE structure on the viscosity of the continuous phase and the effective volume fraction of the dispersed phase.     

Effect of the ratio of maleated polypropylene to organoclay on the structure and properties of TPO-based nanocomposites. Part I: Morphology and mechanical properties

The structure-property relationships of thermoplastic olefin (TPO)-based nanocomposites prepared by melt processing are reported with a main focus on the ratio of maleic anhydride-grafted polypropylene (PP-g-MA) to organoclay. The morphological observations by transmission electron microscopy, atomic force microscopy, and X-ray diffraction are presented in conjunction with the mechanical and rheological properties of these nanocomposites. Detailed quantitative analyses of the dispersed clay particles revealed that the aspect ratio of clay particles decreased as clay content increased but increased as the amount of PP-g-MA increased. Analysis of the elastomer phase revealed that the aspect ratio of the elastomer phase increased in both cases. The presence of clay causes the elastomer particles to become highly elongated in shape and retards the coalescence of the elastomer particles. The modulus and yield strength are enhanced by increasing the PP-g-MA/organoclay ratios. High levels of toughness of the TPO can be maintained when moderate levels of (organoclay) MMT and PP-g-MA are used. The rheological properties suggested that the addition of clay particles and PP-g-MA has a profound influence on the long time stress relaxation of the TPO nanocomposites. Based on these analyses, it is clear that it is important to optimize the ratio of PP-g-MA and organoclay to obtain the desired balance of mechanical properties and processing characteristics for TPO nanocomposites.     

One-pot in situ ball milling preparation of polymer/graphene nanocomposites

A one-pot method which involves peeling graphite nanosheets (GNs) off into graphenes in polymer solution and in situ forming polymer/graphene sheets nanocomposites by using ball milling is presented. Via this approach, nanocomposites based on maleic anhydride grafted poly (ethylene-co-vinyl acetate) (EVA-g-MAH) and graphene sheets comprising one to five layers were accomplished. The resulted EVA-g-MAH/graphene nanocomposites displayed a percolation threshold around 5.0 wt %, much lower than that of the EVA-g-MAH/GNs nanocomposites prepared by direct solution blending (∼ 13.0 wt %). The nanocomposite containing 10 wt % of graphene sheets exhibited a higher maximum decomposition temperature by ∼ 10°C when compared with the virgin polymer and the corresponding nanocomposite loaded with 10 wt % of GNs. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Ultrasonic induced grafting of maleic anhydride onto polypropylene in melt state

This paper presented a model study on maleic anhydride (MAH) grafted polypropylene (PP) performed in melt state through ultrasonic initiation without any chemical initiator and solvent. The structures of PP-g-MAH were characterized by FTIR and ¹³C NMR and the mechanism were discussed. The graft degree (G) was determined by titration using a solution of organic base tetra-butyl ammonium hydroxide (TBAOH) in ethanol, and the effects of ultrasonic intensity, MAH concentration and styrene (St) on G and graft efficiency (G _E ) of MAH were investigated. Results showed that MAH was successfully grafted onto the PP chain and the optimum conditions for grafting were at an ultrasonic intensity of 300 W with a MAH concentration of 25 wt.%, and the maximum G of MAH of 3.34 wt.% was obtained when the molar ratio of St to MAH was 1:1. DSC and XRD were also employed to determine the thermodynamic performance and crystalline structures of the products.