Recycling of polypropylene‐based eco‐composites

BACKGROUND: Renewable resources and recyclable thermoplastic polymers provide an attractive eco‐friendly quality as well as environmental sustainability to the resulting natural fibre‐reinforced composites. The properties of polypropylene (PP)‐based composites reinforced with rice hulls or kenaf fibres were investigated with respect to their recyclability. Rice hulls from rice processing plants and natural lignocellulosic kenaf fibres from the bast of the plant Hibiscus cannabinus represent renewable sources that could be utilized for composites. Maleic anhydride‐grafted PP was used as a coupling agent to improve the interfacial adhesion between fillers and matrix. Composites containing 30 wt% reinforcement were manufactured by melt mixing and their mechanical and thermal properties were determined. The composites were then pelletized and reprocessed by melt mixing. Finally, structure/properties relationships were investigated as a function of the number of reprocessing cycles. RESULTS: It is found that the recycling processes do not induce very significant changes in flexural strength and thermal stability of the composites. In particular PP‐based composites reinforced with kenaf fibres are less sensitive to reprocessing cycles with respect to PP‐based composites reinforced with rice hulls. CONCLUSION: The response of PP‐based composites reinforced with rice hulls or kenaf fibres is promising since their properties remain almost unchanged after recycling processes. Moreover, the recycled composites are suitable for applications as construction materials for indoor applications. In fact, the flexural strength and modulus of these materials are comparable to those of conventional formaldehyde wood medium‐density fibreboards. Copyright © 2008 Society of Chemical Industry     

Melt compounding of polypropylene‐based clay nanocomposites

Polypropylene (PP)‐based nanocomposites containing 4 wt% maleic anhydride grafted PP (PP‐g‐MA) and 2 wt% Cloisite 20A (C20A) were prepared using various processing devices, viz., twin‐screw extruder (TSE), single‐screw extruder (SSE), and SSE with an extensional flow mixer (EFM). Two processing methods were employed: (I) masterbatch (MB) preparation in a TSE (with 10 wt% C20A and clay/compatibilizer ratio of 1:2), followed by dilution in TSE, SSE, or SSE + EFM, to 2 wt% clay loading; (II) single pass, i.e., directly compounding of dry‐blended PP‐g‐MA/clay in TSE, SSE, or SSE + EFM. It has been indicated that the quality of clay dispersion, both at micro‐ and nanolevel, of the nanocomposites depends very much on the operating conditions during processing, such as mixing intensity and residence time, thus affecting the mechanical performance. Besides that the degradation of the organoclay and the matrix is also very sensitive to these parameters. According to results of X‐ray diffraction, field emission gun scanning electron microscopy, transmission electron microscopy, and mechanical tests, the samples prepared with MB had better overall clay dispersion, which resulted in better mechanical properties. The processing equipment used for diluting MB had a marginal influence on clay dispersion and nanocomposite performance. POLYM. ENG. SCI., 47:1447–1458, 2007. © 2007 Society of Plastics Engineers     

Electrical conductivity of carbon‐filled polypropylene‐based resins

Adding conductive carbon fillers to insulating thermoplastic resins increases composite electrical conductivity. Often, as much of a single type of carbon filler is added to achieve the desired conductivity and still allow the material to be molded into a bipolar plate for a fuel cell. In this study, various amounts of three different carbons (carbon black, synthetic graphite particles, and carbon nanotubes) were added to polypropylene resin. The resulting single‐filler composites were tested for electrical resistivity (1/electrical conductivity). The effects of single fillers and combinations of the different carbon fillers were studied via a factorial design. The percolation threshold was 1.4 vol % for the composites containing only carbon black, 2.1 vol % for those containing only carbon nanotubes, and 13 vol % for those containing only synthetic graphite particles. The factorial results indicate that the composites containing only single fillers (synthetic graphite followed closely by carbon nanotubes and then carbon black) caused a statistically significant decrease in composite electrical resistivity. All of the composites containing combinations of different fillers had a statistically significant effect that increased the electrical resistivity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Nanoclay‐reinforced,polypropylene‐based wood–plastic composites

Wood plastic composites (WPCs) are a new class of materials which combine the characteristics of plastic and wood. In appearance, they are similar to wood, but the low stiffness of plastics makes the composite modulus significantly lower than that of solid wood. Increasing the wood content in the WPCs can improve stiffness, but the rate of water absorption also goes up. Here, nanoclay was compounded with wood and plastic using a twin screw extruder to form a three‐component composite to improve the stiffness of WPCs. To overcome the previously observed reduction in strength and increase in the rate of water absorption, different compounding procedures were used. It was found that pre‐compounding wood flour with polymer followed by incorporation of clay in a second step resulted in an increase in stiffness, retention in strength, and a reduction in the rate of water absorption. Thus, adding nanoclays is an alternative for increasing properties instead of adding extra wood flour to a concentration in excess of 55 wt% as this involves processing difficulties. POLYM. ENG. SCI., 50:2013–2020, 2010. © 2010 Society of Plastics Engineers     

Study on polypropylene–polyethylene‐based copolymer solidification

In the present work, nonisothermal crystallization is analyzed. Concretely, we study the solidification process of polypropylene–polyethylene‐based copolymers by means of differential scanning calorimetry (DSC). Several samples with different additives are subjected to artificial aging processes. The calculation of the specific surface energy, σ, is in good accordance with the results reported in the references. The artificial aging is responsible for a slight increase of σ values (i.e., increase of 1.6 kJ · m⁻² for sample A and 0.3 kJ · m⁻² for sample B). On the other hand, the σ value of sample B is considerably lower than that of samples A, C, and D (i.e., 17.3 kJ · m⁻² for sample B versus an average value of 23.0 kJ · m⁻² for the other samples). Microstructure analysis was performed by scanning electronic microscopy (SEM). As shown from the analysis, aging only affects superficial zones because no changes in the morphology of the central zone were detected in the different samples. Sample B shows a different behavior; it was less resistant to fracture. From DSC and SEM measurements, we can state the additive influence on the original sample behavior as well as on the solidification process of polypropylene–polyethylene‐based copolymers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1269–1274, 2000     

Conifer fibers as reinforcing materials for polypropylene‐based composites

Conifer fibers were used to reinforce polypropylene (PP). To improve the compatibility between the conifer fibers and the PP matrix, the fibers were either grafted with maleated PP (MAPP), treated by adding MAPP, or mixed with ethylene/propylene/diene terpolymer (EPDM). The treatments resulted in improved processing, as well as improvements in the thermal and mechanical properties of the resultant composites compared with the composites filled with untreated conifer fibers. Moreover, MAPP grafting and MAPP treating displayed more obvious benefits than EPDM treating in terms of thermal properties, processing flowability, and tensile strength improvements. EPDM treating also produced more significant benefits than either MAPP grafting or MAPP treating in terms of impact strength and tensile elongation improvements. These improvements were attributed to surface coating of the fibers when EPDM was used. In addition, the effect of the concentration of the conifer fibers on the properties of the composites and the difference between MAPP grafting and MAPP treating were evaluated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2833–2841, 2001     

Characterization of contamination effects for two polypropylene‐based materials

In this work, contamination effects are studied on two polypropylene‐based materials. These effects were identified on the molecular weight and on rheological and mechanical properties. Model contaminants chosen in this study were ethylene glycol and engine oil. They were added during the extrusion process to simulate the degradation due to contaminants. To quantify contamination effects and to correlate them with the microstructure evolution, scanning electron microscope (SEM) analyses were also conducted. The analysis of the different obtained results led to a better understanding of the mechanisms involved in the contamination process. Contaminants slightly affect the rheological properties, whereas mechanical properties are more influenced. These observations are confirmed by the modification of the fractured surfaces of the materials due to the presence of contaminants observed on SEM micrographs. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Crystalline phase and electrical properties of lead‐free piezoelectric KNN‐based films with different orientations

Lead‐free piezoelectric 0.915K_0.5Na_0.5NbO₃‐0.075BaZrO₃‐0.01Bi_0.5Na_0.5TiO₃ (KNN‐BZ‐BNT) films were grown on Nb‐doped SrTiO₃ substrates with different orientations. The thin films show highly preferential orientations in accordance with the orientations of single crystalline substrates. The films all exhibit a weak contrast and remarkable homogeneity in the local static out‐of‐plane piezoresponse phase images, suggesting a strong self‐polarization. Combining with the analysis of XRD‐RSM, TEM and PFM, the crystalline phase of our samples was determined to be rhombohedral, which has the spontaneous polarization along [111] direction. Thus, the (100)‐oriented film demonstrates the most superior piezoelectric properties. Our detailed studies on structural and electrical properties of KNN‐BZ‐BNT films further clarify the structure‐property relationship and make a step closer to use this lead‐free material for many piezoelectric applications.     

Rheological and mechanical characterization of polypropylene‐based wood plastic composites

The aim of this article is to investigate the influence of filler content and temperature on the rheological, mechanical, and thermal properties of wood flour polypropylene composites (WPCs). Testing WPCs at high temperatures and percentages of filler is extremely challenging because of reduced linear viscoelastic region, high viscosity, and degradation. In this work, a complete characterization of WPCs with different filler percentages (0–70 wt%) has been made. Rheological tests are performed at 170°C for the WPCs and in the 170–200°C range for neat polypropylene. A single master curve is obtained using two shift factors that can be described by a modified Eilers model and a Williams‐Landel‐Ferry equation. This master curve, fitted with a Carreau‐Yasuda model, can be very useful for predicting the viscosity of WPCs at temperatures that are typically used during processing and for any percentage of filler. POLYM. COMPOS., 37:3460–3473, 2016. © 2015 Society of Plastics Engineers     

Impact modification of polypropylene‐based composites using surface‐coated waste rubber crumbs

Blends of maleated polypropylene (MAPP) with high contents of waste rubber powder, namely ground tire rubber and waste ethylene propylene diene monomer (EPDM) powder, were used as impact modifiers for polypropylene (PP) based composites with different reinforcements (hemp, talc, and milled glass fiber). Adding reinforcements led to increase in modulus (tensile, flexural, and torsion moduli) of PP, while its impact strength decreased noticeably. Impact modification of PP‐based composites was successfully performed via inclusion of MAPP/waste rubber compounds, especially compounds containing waste EPDM powder. Inclusion of such impact modifiers increased impact strength of composites over 80%. The effects of impact modification were more significant for hemp‐ and glass‐filled composites compared to composites containing talc. However, slight decrease in tensile, flexural, and torsion moduli (up to 30%) of the composites was also observed after inclusion of impact modifiers. POLYM. COMPOS., 35:2280–2289, 2014. © 2014 Society of Plastics Engineers     

The influence of carbon‐based fillers on the flammability of polypropylene‐based co‐extruded wood‐plastic composite

Comparative analysis of the effect of carbon‐based fillers with different particle sizes and morphologies on the flammable properties of a co‐extruded wood‐plastic composite is performed. Five carbon‐based fillers, namely carbon black, carbon nanotubes, graphite, expandable graphite, and carbon fibers were loaded into the shell layer of the composite. The flammability was characterized by using the cone calorimeter technique. The nanosized fillers, carbon black and carbon nanotubes, had a larger impact on the peak of the heat release rate, decreasing it by 16% and 17%, respectively. The samples with graphite, expandable graphite, and carbon fibers, decreased the peak of the heat release rate by 10%, 6%, and 11%, respectively. The total heat release decreased slightly for all the samples, except for the carbon fibers–wood‐plastic composite. The effective heat of combustion decreased also slightly, and carbon monoxide production increased for all the studied composites. Copyright © 2015 John Wiley & Sons, Ltd.     

Polypropylene/polypropylene‐grafted acrylic acid blends for multilayer films: Preparation and characterization

Polypropylene (PP) was functionalized with acrylic acid (AA) and styrene (st) as a comonomer by means of a radical‐initiated melt‐grafting reaction. FTIR, ESCA, and ¹H‐NMR spectroscopies were used to characterize the formation of polypropylene grafted with acrylic acid (PP‐g‐AA) and polypropylene grafted with acrylic acid and styrene (PP‐g‐AAst). The content of AA grafted onto PP was determined by using volumetric titration. Blends of PP with 0–100 wt % of PP‐g‐AA were prepared by melt mixing. The effect of the modified polymer content on the surfaces of cast films was characterized through FTIR–ATR and ESCA analysis as well as contact‐angle, wetting‐tension, and ink‐adhesion measurements. The influence of the content of AA on the melting and crystallization temperature of PP was investigated by DSC. The contact angles of water on cast‐film surfaces of PP/PP‐g‐AA blends decreases with increasing modified polymer content and decreasing PP‐g‐AA molecular weight. A notorious improvement on wetting tension was observed with increasing modified polymer content and decreasing PP‐g‐AA molecular weight. From FTIR–ATR and ESCA spectra of the blends, a calculation was made of the carbonyl index on the films' surfaces. It was found that the higher the carbonyl index, the lower the contact‐angle value for the polypropylene blends. An increase in crystallization temperature of PP was observed when AA monomers were grafted into PP and with increasing PP‐g‐AA content in the blend, probably caused by a nucleation effect of AA monomers that would improve the crystallization capability of PP. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1497–1505, 2001     

Thermal and fire degradation of recycled and polluted polypropylene‐based materials

In this study, the effect of processing cycles and two pollutants (engine oil (HM) and ethylene glycol (EG)) on the thermal and rheological properties of polypropylene‐based materials (108MF97 and 7510) has been studied. It was investigated if polymers coming from bumper face bar could keep their properties and can be reused after recycling. The different results demonstrate that the two polymers that were polluted and recycled do not show any decrease of their intrinsic properties. Moreover, for one of the two polymers (108MF97), the presence of engine oil enables to increase the thermal stability and reaction to fire. Finally, it appears that the reuse of such polymers is possible. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

New synthesis methods for polypropylene‐co‐ethylene‐propylene rubber

In this research, the reinforcement of polypropylene (PP) was studied using a new method that is more practical for synthesizing polypropylene‐block‐poly(ethylene‐propylene) copolymer (PP‐co‐EP), which can be used as a rubber toughening agent. This copolymer (PP‐co‐EP) could be synthesized by varying the feed condition and changing the feed gas in the batch reactor system using Ziegler–Natta catalysts system at a copolymerization temperature of 10°C. The ¹³C‐NMR tested by a 21.61‐ppm resonance peak indicated the incorporation of ethylene to propylene chains that could build up the microstructure of the block copolymer chain. Differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and dynamic mechanical analysis (DMA) results also confirmed these conclusions. Under these conditions, the morphology of copolymer trapped in PP matrix could be observed and the copolymer T_g would decrease when the amount of PP‐co‐EP was increased. DMA study also showed that PP‐co‐EP is good for the polypropylene reinforcement at low temperature. Moreover, the PP‐co‐EP content has an effect on the crystallinity and morphology of polymer blend, i.e., the crystallinity of polymer decreased when the PP‐co‐EP content increased, but tougher mechanical properties at low temperature were observed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3609–3616, 2007     

Preparation of polypropylene‐based nanocomposites using nanosized MCM‐41 as support and in situ polymerization

MCM‐41 nanoparticles were used for preparing nanocomposites through the in situ polymerization of propylene. The performance of the catalytic system and the final properties of the materials obtained are highly dependent on the methodology used for impregnation of the catalyst onto the support particles, and therefore an optimization study for the impregnation methodology of the catalyst (Me₂Si(Ind)₂ZrCl₂) was carried out. Two different methodologies were used; the results in terms of catalytic activity and polymer molecular masses indicated that the most promising one involved the pre‐activation of the catalyst with the cocatalyst, methylaluminoxane, followed by impregnation onto the MCM‐41 nanoparticles. Thus, an optimized route for the preparation of polypropylene nanocomposites achieving significant improvements in catalyst activity was developed. The nanocomposite materials were characterized by GPC, TGA and DSC. The dispersion state and the size of the nanoparticles incorporated in the polypropylene matrix were investigated by transmission electron microcopy. Additionally, this methodology allows simultaneous control of the desired amount of support and the concentration of catalyst to be used in the in situ polymerization. © 2015 Society of Chemical Industry     

Synthesis and characterization of polypropylene‐grafted gelatin

Modification of polypropylene (PP) has been successfully carried out by graft copolymerization of gelatin, by chemical method using benzoyl peroxide (BPO) as radical initiator. PP was preirradiated by gamma rays at a constant dose rate of 3.40 kGy/h before grafting to introduce hydroperoxide groups. Optimum conditions pertaining to maximum percentage of grafting were evaluated as a function of different reaction parameters. Maximum percentage of grafting of gelatin (115%) was obtained at BPO concentration = 4.132 × 10^?2 mol/L in 120 min at 70°C using 30 mL of water. Characterization of PP‐g‐gelatin was carried out through FTIR, thermogravimetric analysis, and scanning electron microscopy. Swelling studies were carried out in pure, binary, ternary, and quaternary solvent systems comprising distilled water, ethanol, dimethylsulphoxide (DMSO), and N,N‐dimethylformamide (DMF) in different ratios. Maximum swelling of PP‐g‐gelatin (both composite and true graft) was observed in pure solvents that is, DMSO followed by DMF, ethanol, and water and was higher than that observed in the mixed solvent system. Water retention studies of unmodified PP, that is, pristine PP and PP‐g‐gelatin (both composite and true graft) were investigated at different time periods, temperatures and pH. Maximum % water retention for PP‐g‐gelatin (composite; 170%) was observed in 8 h at 50°C in neutral medium (pH = 7). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Microstructure dependent properties of polypropylene‐clay nanocomposites

The mechanical properties of melt processed polypropylene‐montmorillonite nanocomposites were studied as a function of clay content. The measurement of tensile properties at room temperature and dynamic mechanical properties over a wide temperature range reveal a decrease in modulus and tensile strength of the composite with increasing clay content. The origins of this anomalous result were examined in detail using X‐ray diffraction and differential scanning calorimeter, which averaged the microstructure over reasonable specimen volumes. Micromechanical models could be used to adequately describe the composite properties, provided appropriate properties for the matrix and particle were used. The matrix properties were found to affect the average properties significantly. © Wiley Periodicals, Inc. J Appl Polym Sci 103: 204–210, 2007     

Effects of carbon fillers on tensile and flexural properties in polypropylene‐based resins

A potential application for conductive resins is in bipolar plates for use in fuel cells. The addition of carbon filler can increase the electrical and thermal conductivities of the polymer matrix but will also have an effect on the tensile and flexural properties, important for bipolar plates. In this research, three different types of carbon (carbon black, synthetic graphite, and carbon nanotubes) were added to polypropylene and the effects of these single fillers on the flexural and tensile properties were measured. All three carbon fillers caused an increase in the tensile and flexural modulus of the composite. The ultimate tensile and flexural strengths decreased with the addition of carbon black and synthetic graphite, but increased for carbon nanotubes/polypropylene composites due to the difference in the aspect ratio of this filler compared to carbon black and synthetic graphite. Finally, it was found that the Nielsen model gave the best prediction of the tensile modulus for the polypropylene based composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and properties of polypropylene‐asphaltene composites

In this study, novel composite materials of polypropylene (PP) with asphaltenes taken from Arab heavy atmospheric residue were prepared and characterized. Composites with various relative amounts of asphaltenes to PP were formed using the melt‐mixing technique. The chemical structure, crystalline form, and morphology of these materials were examined using Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), and scanning electron microscopy (SEM) measurements. Their thermal properties were measured with differential scanning calorimetry (DSC), their thermal degradation characteristics with thermogravimetric analysis (TGA), and the mechanical properties using an Instron dynamometer. It was found that the crystalline and chemical structure of PP is not affected by the presence of asphaltenes, whereas the thermal stability, crystallinity, and tensile mechanical properties are enhanced with the amount of asphaltenes. Particularly, the addition of 5 wt% asphaltenes could improve tensile strength and the Elastic modulus by almost 10%. Better dispersion is achieved at relative low percentages of asphaltenes. It was found that the optimum amount of asphaltenes to result in composites with good dispersion, enhanced thermal stability, tensile strength, and relative crystallinity was 5 wt%. Most of these properties seem to deteriorate when the amount of asphaltenes added is high (i.e., 10%–15%). Therefore, a new use of a by‐product of the petroleum refinery industry is proposed resulting in improved properties of a commodity polymer. POLYM. COMPOS., 38:1957–1963, 2017. © 2015 Society of Plastics Engineers     

Exfoliation targeted toughness enhancement in polypropylene‐blend‐ montmorillonite nanocomposites

BACKGROUND: Both exfoliated and toughened polypropylene‐blend‐montmorillonite (PP/MMT) nanocomposites were prepared by melt extrusion in a twin‐screw extruder. Special attention was paid to the enhancement of clay exfoliation and toughness properties of PP by the introduction of a rubber in the form of compatibilizer toughener: ethylene propylene diene‐based rubber grafted with maleic anhydride (EPDM‐g‐MA). RESULTS: The resultant nanocomposites were characterized using X‐ray diffraction, atomic force microscopy, scanning electron microscopy, thermogravimetric analysis, dynamic mechanical analysis and Izod impact testing methods. It was found that the desired exfoliated nanocomposite structure could be achieved for all compatibilizer to organoclay ratios as well as clay loadings. Moreover, a mechanism involving a decreased size of rubber domains surrounded with nanolayers as well as exfoliation of the nanolayers in the PP matrix was found to be responsible for a dramatic increase in impact resistance of the nanocomposites. CONCLUSION: Improved thermal and dynamic mechanical properties of the resultant nanocomposites promise to open the way for highly toughened super PPs via nanocomposite assemblies even with very low degrees of loading. Copyright © 2008 Society of Chemical Industry