Comparison of the effect of mica and talc and chemical coupling on the rheology,morphology, and mechanical properties of polypropylene composites

The effect of filler types of mica and talc on the oscillatory shear rheological properties, mechanical performance, and morphology of the chemically coupled polypropylene composites is studied in this work. The Maleic Anhydride grafted Polypropylene (MAPP) was used as an adhesion promoter for coupling mineral particles with the polypropylene matrix. The samples were prepared by a co‐rotating, L/D = 40, 25 mm twin screw extruder. The tensile tests carried out on the injection molded samples showed a reinforcing effect of talc up to 20 wt% on the Polypropylene (PP). The tensile strength of PP‐mica composites showed a slight decrease at all percentages of mica. The effect of chemical coupling by using MAPP on the tensile strength was more pronounced in increasing the tensile strength for PP‐mica than PP‐talc composites. The complex viscosity curve of pure PP and the composites, showed a Newtonian plateau (η₀) up to 30 wt% at low frequency terminal zone. By increasing the filler content to 40 and 50 wt%, the complex viscosity at very low shear rates sharply increased and showed yield behavior that can be due to the formation of filler particles networks in the melt. At the optimum amount of coupling agent, a minimum in cross over frequency curve against MAPP content is observed. The optimum amount of coupling agent for PP‐talc composites is about 1.5%, and about 3% for PP‐mica formulations. The analysis of viscosity behavior at power‐law high region, revealed the more shear thinning effect of mica than talc on the PP matrix resin. Copyright © 2009 John Wiley & Sons, Ltd.     

Accelerated weathering of unbleached and bleached Kraft wood fibre reinforced polypropylene composites

In this paper, combined moisture/ultraviolet (UV) weathering performance of unbleached and bleached Kraft wood fibre reinforced polypropylene (PP) composites was studied. Composites containing 40 wt% fibre with 3 wt% of a maleated polypropylene (MAPP) coupling agent were fabricated using extrusion followed by injection moulding. Composite mechanical properties were evaluated, before and after accelerated weathering for 1000 h, by tensile and impact testing. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were also carried out to assess the changes occurring during accelerated weathering. Bleached fibre composites initially showed higher tensile and impact strengths, as well as higher thermal stability and greater crystallinity. During accelerated weathering, both unbleached and bleached fibre composites reduced tensile strength (TS) and Young's modulus (YM), with the extent of the reduction found to be similar for both unbleached and bleached fibre composites. Evidence supported that the reduction of TS and YM was due to PP chain scission, degradation of lignin and reduced fibre-matrix interfacial bonding.     

Influence of surface modification of fillers and polymer on flammability and tensile behaviour of polypropylene-composites

An intumescent system consisting of ammonium polyphosphate (APP) as an acid source and blowing agent, pentaerythritol (PER) as a carbonific agent and natural zeolite (clinoptilolite, Gördes II) as a synergistic agent was used in this study to enhance flame retardancy of polypropylene (FR-PP). Zeolite was incorporated into flame retardant formulation at four different concentrations (1, 2, 5, and 10 wt%) to investigate synergism with the flame retardant materials. Filler content was fixed at 30 wt% of total amounts of flame retardant PP composites. Zeolite and APP were treated with two different coupling agents namely, 3-(trimethoxysilyl)-1-propanethiol and (3-aminopropyl)-triethoxysilane for investigation of the influence of surface treatments on mechanical properties and flame retardant performance of composites. Maleic anhydride grafted polypropylene (MAPP) was used for making polypropylene hydrophilic. Flammability of FR-PP composites was measured by the determination of limiting oxygen index (LOI). The LOI values reached to a maximum value of 41% for mercapto silane treated APP:PER (2:1) PP composite containing 5 wt% zeolite. The tensile strength of composites was increased by the addition of MAPP and elongation at break of composites was increased with silane treatments.     

Molecular orientation,crystallinity, and flexural modulus correlations in injection molded polypropylene/talc composites

In order to promote better understanding of the structure‐mechanical properties relationships of filled thermoplastic compounds, the molecular orientation and the degree of crystallinity of injection molded talc‐filled isotactic polypropylene (PP) composites were investigated by X‐ray pole figures and wide‐angle X‐ray diffraction (WAXD). The usual orientation of the filler particles, where the plate planes of talc particles are oriented parallel to the surface of injection molding and influence the orientation of the α‐PP crystallites was observed. The PP crystallites show bimodal orientation in which the c‐ and a*‐axes are mixed oriented to the longitudinal direction (LD) and the b‐axis is oriented to the normal direction (ND). It was found that the preferential b‐axis orientation of PP crystallites increases significantly in the presence of talc particles up to 20 wt% in the composites and then levels‐off at higher filler content. WAXD measurements of the degree of crystallinity through the thickness of injection molded PP/talc composites indicated an increasing gradient of PP matrix crystallinity content from the core to the skin layers of the molded plaques. Also, the bulk PP crystallinity content of the composites, as determined by DSC measurements, increased with talc filler concentration. The bulk crystallinity content of PP matrix and the orientation behavior of the matrix PP crystallites and that of the talc particles in composites are influenced by the presence of the filler content and these three composite's microstructure modification factors influence significantly the flexural moduli and the mechanical stiffness anisotropy data (E_LD/E_TD) of the analyzed PP/talc composites. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of Silane Coupling Agent and Compatibilizer on Properties of Short Rossells Fiber/Poly(propylene) Composites

Rossells fiber reinforced polypropylene composites were prepared by melt mixing. The fiber content was 20 wt%. Octadecyltrimethoxysilane (OTMS) and maleic anhydride grafted polypropylene (MAPP) were used to improve the adhesion between poly(propylene) (PP) and the fiber. The mechanical, rheological, and morphological properties, and heat distortion temperature (HDT) of the composites were investigated. Tensile strength, impact strength, flexural strength and HDT of MAPP modified PP composites increased with an increase in MAPP content. However, no remarkable effect of MAPP content on the Young's modulus of the composites was found. OTMS resulted in small decreases of tensile strength and Young's modulus, and increase in impact strength. Scanning electron micrographs revealed that MAPP enhanced surface adhesion between the fiber surface and PP matrix.     

Evaluating of reinforcing effect of Ceratonia Siliqua for polypropylene: Tensile,flexural and other properties

The aim of this study is to investigate the reinforcing effect of Ceratonia siliqua (CS) powder as a novel natural filler for polypropylene (PP) based composites. CS powder up to 20 wt% was filled into PP matrix by using high speed thermo kinetic mixer. Mechanical and thermal properties of CS filled PP based composites were investigated by tensile and three point bending test, dynamic mechanical analysis, thermogravimetric analysis, differential scanning calorimetry analysis, fourier transform infrared analysis, and thermomechanical analysis. Morphology of the composites was also investigated by scanning electron microscopy. By filling 5% and 10% of CS into PP, tensile strength and flexural strength of PP increased by about 32 and 23%, respectively. This indicates that CS has a great potential to be used as reinforcing filler for PP composites. CS filling into PP led to lower coefficient of thermal expansion values which could help preventing the thermal expansion.     

Novel high-strength,micro fibrillated cellulose-reinforced polypropylene composites using a cationic polymer as compatibilizer

Novel high-strength, micro-fibrillated cellulose (MFC)-reinforced polypropylene (PP) composites were prepared using maleic anhydride polypropylene (MAPP) and a cationic polymer having a primary amino group (CPPA) as coupling agents. Un-dried kraft pulp was micro-fibrillated into nano- to submicron-wide fibrils by kneading with powdered PP and the coupling agents via a twin-screw extruder. The composites were prepared by injection molding. The MFC-reinforced PP composites containing both coupling agents MAPP and CPPA (combination system) showed extremely high mechanical strength compared with the MFC-reinforced composite containing only MAPP. The tensile strength of a 30 wt% MFC-PP composite containing the combination system was 27 % higher than that of the composite containing only MAPP, and more than 60 % higher than that of neat PP. In addition, the heat distortion temperature, under a 1.82-MPa flexural load, of the composite with the combination system was 17 °C higher than that of the composite with MAPP only, and 34 °C higher than that of neat PP. The anisotropy of the modulus and strength in the injection-molded MFC composites was lower than that of glass fiber-reinforced PP.     

Effect of hybrid fillers on the mechanical behavior of polypropylene based hybrid composites

The present study investigates the effect of hybrid fillers such as graphene nanoplatelets (GnPs) and Titanium di-oxide (TiO₂) in polypropylene (PP) composites on the mechanical properties. The compatibilizing agent of Maleic anhydride grafted polypropylene (MAPP) are used in the polypropylene based composites to increase the interfacial adhesion between matrix and fillers. The experiments are designed according to L₁₆ orthogonal array (OA) based design of experiments (DOE). The parameters selected for this study are GnPs, TiO₂ and MAPP with four different levels are used.By using Orthogonal array and Taguchi based experimental design, the performance characteristics of tensile modulus, tensile strength, elongation at break and toughness can be analyzed with more objective through a small set of experiments.Taguchi based analysis are used to find out the optimal parameters to maximize the tensile properties for the GnPs and TiO₂ reinforced PP hybrid composites. Further, analysis of variance (ANOVA) is investigated to identify the most significant parameters which influence the mechanical properties.From the analysis it was found that the optimal parameters of 3 ?wt% GnPs, 2 ?wt% TiO₂ and 6 ?wt% MAPP for maximum tensile modulus and tensile strength. The most significant parameter for tensile modulus and tensile strength is GnPs followed by TiO₂ and MAPP according to ANOVA analysis.     

Development of continuous process enabling nanofibrillation of pulp and melt compounding

Microfibrillated cellulose (MFC), a mechanically fibrillated pulp mostly consisting of nanofibrils, is a very attractive material because of its high elastic modulus and strength. Although much research has been done on composites of MFC and polypropylene (PP), it has been difficult to produce such composites at an industrial level because of the difficulties in using MFC in such composites are not only connected to the polarity (that can be improved with compatibilizers), but also with the challenge to make a homogeneous blend of the components, and also the low temperature stability of cellulose that could cause problems during processing. We developed a new processing method which enables continuous microfibrillation of pulp and its melt compounding with PP. Never-dried kraft pulp and powdered PP were used as raw materials to obtain MFC by kneading via a twin-screw extruder. Scanning electron microscopy showed nano to submicron wide fibers entangled in the powdered PP. MFC did not aggregate during the melt compounding process, during which the water content was evaporated. Maleic anhydride polypropylene (MAPP) was used as a compatibilizer to reinforce interfacial adhesion between the polar hydroxyl groups of MFC and non-polar PP. We investigated the effect of MAPP content on the mechanical properties of the composite, which were drastically improved by MAPP addition. Needle-leaf unbleached kraft pulp (NUKP)-derived MFC composites had better mechanical properties than needle-leaf bleached kraft pulp (NBKP)-derived MFC composites. Injection molded NUKP-derived MFC composites had good mechanical and thermal properties. The tensile modulus of 50 wt% MFC composite was two times, and the tensile strength 1.5 times higher than that of neat PP. The heat distortion temperature of 50 wt% MFC content composite under 1.82 MPa flexural load was increased by 53 °C, from 69 to 122 °C. This newly developed continuous process using powder resin has the potential for application at an industrial level.     

Mechanical properties and characteristic of surface treated bamboo fiber reinforced PP/PS blends

Bamboo fiber (BF) as organic filler is characterized by mechanical properties analysis and morphology examination for polypropylene (PP) and polystyrene (PS) matrix blends. Effects of different filler content on tensile strength, flexural properties, and impact strength are proposed. It is observed from scanning electron microscopy (SEM) studies that addition of BF is beneficial in increasing mechanical strength via increasing the interface dispersed phase. The optimum tensile properties and impact properties of BF content were at 40 wt% for PP/PS/BF composite on melt mixing conditions. The results showed a significant improvement in mechanical properties of PP/PS/BF ternary blend composite. Comparing with untreated BF, content of carbon and nitrogen of treated BF decreased to 66.57 and 2.31%, oxygen content increased to 21.07%, and silicon content increased from 0 to 10.04%. The element ratio of O/C, N/C, and Si/C changed to 31.65, 3.47, and 15.08, respectively.     

Effect of long fiber thermoplastic extrusion process on fiber dispersion and mechanical properties of viscose fiber/polypropylene composites

Viscose fiber reinforced polypropylene (PP/VF) composites were manufactured using long fiber thermoplastic (LFT) extrusion techniques with two different methods namely LFT‐l and LFT‐2. The compatibilizer [maleated polypropylene (MAPP)] and dispersing agent [stearic acid (SA)] were added to the PP/VF in order to improve the fiber dispersion and interfacial adhesion. The PP/VF composites manufactured using LFT‐2 showed better fiber dispersion with higher tensile and flexural properties compared to the composites manufactured using LFT‐1 method. Similarly, the impact strength and toughness of the LET‐2 composites showed an improvement of 36 and 20% than LFT‐1 whereas the average fiber length of composites was decreased from 6.9 mm to 4.4 mm because of the increase in shear energy as a result of residence time. Further, the addition of SA and MAPP to LFT‐2 process has significantly improved the fiber dispersion and mechanical performance. The fiber dispersion and fracture behavior of the LFT‐1 and LFT‐2 composites were studied using scanning electron microscopy analysis. The Fourier transformation infrared spectra were also studied to ascertain the existence of type of interfacial bonds. Copyright © 2015 John Wiley & Sons, Ltd.     

Synergistic effect between a char forming agent (CFA) and microencapsulated ammonium polyphosphate on the thermal and flame retardant properties of polypropylene

The synergistic effect between a char forming agent (CFA) and microencapsulated ammonium polyphosphate (MAPP) on the thermal and flame retardancy of polypropylene (PP) are investigated by limiting oxygen index (LOI), UL‐94 test, cone calorimetry, thermogravimetric analysis (TGA), scanning electron micrograph (SEM), and water resistance test. The results of cone calorimetry show that heat release rate peak (PHRR), total heat release (THR), and the mass loss of PP with 30 wt% intumescent flame retardant (IFR, CFA/MAPP = 1:2) decreases remarkably compared with that of pure PP. The HRR, THR, and mass loss decrease, respectively from 1140 to 100 kW/m², from 96 to 16.8 MJ/m², and from 100 to 40%. The PP composite with CFA/MAPP = 1:2 has the best water resistance, and it can still obtain a UL‐94 V‐0 rating after 168 hr soaking in water. Copyright © 2008 John Wiley & Sons, Ltd.     

Thermo-oxidative stability of polypropylene/layered silicate nanocomposites

Several series of experiments were carried out to check the effect of components on the stability of PP/layered silicate nanocomposites. The amount of organophilic montmorillonite (OMMT) changed between 0 and 6, while that of maleated polypropylene (MAPP) between 0 and 50 vol%. The composites were prepared in an internal mixer at 190 °C. Mixing speed and time were changed to study the effect of processing conditions on stability. The structure of the samples was characterised by various methods, while stability by the induction time of oxidation (OIT), the onset temperature of degradation (OOT) and by colour. Contrary to numerous claims published in the literature, which indicate the positive effect of layered silicates on the stability of polymer nanocomposites, our results clearly proved that both OMMT and MAPP accelerate degradation during processing and deteriorate the properties of PP composites. Residual stability decreases drastically with increasing amounts of both components, chain scission leads to the decrease of viscosity and to inferior strength and deformability. In spite of expectations, the effect of the components is independent of each other. Discoloration is caused mainly by the inherent colour of the filler and it decreases with increasing exfoliation. The most probable reason for decreased stability is the reaction of the components with the stabilisers, but this explanation needs further verification. Processing conditions influence degradation considerably, increasing shear rate and longer residence times lead to more pronounced degradation. The basic stabilization of commercial grade polypropylenes is insufficient to protect the polymer against degradation and without additional stabilization processing under normal conditions results in products with inferior quality.     

Structures and properties of the compression-molded istactic-polypropylene/talc composites: Effect of cooling and rolling

Talc-loaded isotactic polypropylene (iPP) composites with various contents of talc were fabricated by compression molding, following slow- and fast-cooling processes, to obtain slow-cooled samples (SCS) and fast-cooled samples (FCS), respectively. Lamellar thickness of the α-crystal of iPP in the SCS is observed to be larger than that in the FCS by X-ray diffraction study. Rolled fast-cooled samples (RFCS) were also prepared at 25 °C in order to examine the crystal growth of iPP. An epitaxial growth mechanism of the α-crystal of iPP from the talc crystal is proposed. Surface of talc-loaded FCS appears with a smaller particle size than that of talc-loaded SCS and RFCS as observed by a scanning electron microscope. Young’s modulus and tangent modulus of FCS are found lower than those of SCS with the addition of talc up to 20 wt% and higher above this concentration, except microhardness which is higher in SCS at all contents of talc. From thermal studies, talc-loaded SCS and FCS are found to show higher melting temperature than the neat samples. Effect of cooling and rolling on the structures and properties of the fabricated composites are elaborately discussed.     

Influence of thermal and UV treatment on the polypropylene/graphite composite

Electrically conductive polypropylene/graphite (PP/graphite) composites were prepared via blending granulated PP with maleic anhydride grafted PP and natural graphite. Electrical conductivity of prepared samples containing either 65, 70, or 75 wt% of graphite was measured and the most conductive sample containing 75 wt% of graphite was exposed to UV irradiation for 1 and 24 h or thermally treated at 170 °C for 1 h. The influence of thermal and UV exposure on the structural and electrical changes in such treated samples was studied. Local current measurements on the surface were made using scanning spreading resistance microscopy and morphology of the surface was studied by atomic force microscopy. X-ray diffraction analysis, infrared and Raman spectroscopy were also used for the structural characterization. Properties of treated and untreated samples are compared and differences are discussed.     

Enhanced mechanics in injection molded isotactic polypropylene/polypropylene random copolymer blends via introducing network-like crystal structure

The crystallization behavior, rheological behavior, mechanical properties and microstructures of injection molded isotactic polypropylene(i PP), polypropylene random copolymer(co-PP) and i PP/co-PP blends were investigated. Differential scanning calorimetry(DSC) and dynamic rheological analysis illustrated that i PP and co-PP were compatible in the blends and co-PP uniformly dispersed in the i PP phase. Polarizing optical microscope(POM) was adopted to observe the crystal size and morphology evolution. The results of mechanical properties and scanning electron microscopy(SEM) indicated that the crystal size of i PP in i PP/co-PP blends(10 wt% co-PP + 90 wt% i PP and 30 wt% co-PP + 70 wt% i PP) radically decreased after the incorporation of co-PP. During crystallization, the molecular chain segments of co-PP could penetrate i PP spherulites and form a network-like crystalline structure. The network-like crystal structure could effectively transmit stress and consume more energy to overcome intermolecular forces to resist stretching. In this way, the strength would improve to a certain degree. The impact fracture mechanism of i PP/co-PP blends is quasi ductile fracture by multiple crazes. Our work discovered that the blends containing 10 wt% and 30 wt% of co-PP exhibited prominent toughness and reinforcement.     

Dynamic Mechanical Behavior of PP/PET/MAPP Blends Filled with Glass Beads

PP/PET/MAPP blends have been filled with 50 wt% of glass beads. The orientation of the PP crystalline phase, the crystallization behavior and the dynamic mechanical response of these materials have been analyzed. The dynamic mechanical response is strongly affected by the presence of the glass beads, being possible to detect the effect of PET and MAPP on the storage modulus and loss factor values. Moreover, the alpha relaxation of the composites is visibly affected by thermal treatments.     

Synergistic improvement of fire retardancy and mechanical properties of ferrocene‐based polymer in intumescent polypropylene composite

The ferrocene‐based polymer (PDPFDE) accompanied with traditional intumescent flame retardant (IFR) system (ammonium polyphosphate (APP)/pentaerythritol (PER) = 3/1, mass ratio) has been used as additive flame retardant in polypropylene (PP), aiming to lower the total loading amount. The thermal stability and fire retardant properties were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), vertical combustion (UL‐94), and cone calorimetry (CONE). The fire retardant mechanism was studied by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. The results showed that the PP1 with 25 wt% IFR only passed the UL‐94 V‐1 rating, but the PP6 loaded by 0.5 wt% PDPFDE and 22.5 wt% IFR possessed an LOI value of 28.5% and passed the UL‐94 V‐0 rating; the peak heat release rate (pHRR) and total heat release (THR) are decreased by 63% and 43%, respectively, compared with pure PP. In addition, the char residue of PP6 manifested a very compact and smooth surface, indicating a more effective barrier layer. Meanwhile, it was interesting that the addition of PDPFDE evidently improved the impact strength and elongation at break of PP/IFR composites.     

Dispersion evaluation of microcrystalline cellulose/cellulose nanofibril-filled polypropylene composites using thermogravimetric analysis

Microcrystalline cellulose-filled polypropylene (PP) composites and cellulose nanofiber-filled composites were prepared by melt blending. The compounded material was used to evaluate dispersion of cellulose fillers in the polypropylene matrix. Thermogravimetric analysis (TG) and mechanical testing were conducted on composites blended multiple times and the results were compared with single batch melt blended composites. The residual mass, tensile strength, and coefficient of variance values were used to evaluate dispersion of the microcrystalline cellulose fillers in the PP matrix. The potential of using TG to evaluate cellulose nanofiber-filled thermoplastic polymers was also investigated and it was found that the value and variability of residual mass after TG measurements can be a criterion for describing filler dispersion. A probabilistic approach is presented to evaluate the residual mass and tensile strength distribution, and the correlation between those two properties. Both the multiple melt blending and single batch composites manufactured with increased blending times showed improved filler dispersion in terms of variation and reliability of mechanical properties. The relationship between cellulose nanofiber loading and residual mass was in good agreement with the rule of mixtures. In this article, the authors propose to use a novel method for dispersion evaluation of natural fillers in a polymer matrix using TG residual mass analysis. This method can be used along with other techniques such as scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD) for filler dispersion evaluation in thermoplastic composites.     

A holistic evaluation of the influence of shear rates and matrix viscosity on the properties of polypropylene/multi-walled carbon nanotubes composites

In this work, a comparative study on the electrical, morphological, and thermal properties of polypropylene/multiwalled carbon nanotubes (PP/CNT) composites which were prepared by three different processing methods, such as compression molding (CM, shear rate: ~0 s⁻¹), conventional injection molding (CIM, shear rate: ~10² s⁻¹), and microinjection molding (μIM, shear rate: ~10⁵ s⁻¹), was reported. The difference in shear rates among these processing methods and matrix viscosity would significantly affect the state of filler distribution, thereby determining the properties of subsequent moldings. Electrical conductivity results showed that the percolation threshold of PP/CNT moldings followed a trend of μIM > CIM > CM. A higher degree of CNT orientation and a better filler distribution were achieved under the influence of higher shearing conditions, as corroborated by scanning electron microscope observations and Raman spectral analysis. Moreover, increasing filler concentrations played a positive role in improving the thermal stability of PP/CNT composites and the formation of CNT network was believed to be a contributing factor.