PP Composites Research Articles

Effects of nanoclay cloisite 20A and alkali treatments on structure-property relationships of bagasse/recycled polypropylene nanocomposites

This study was aimed at evaluating the individual and combined effects of organically modified nanoclay cloisite 20A and alkali treatments on the valorization of totally waste-based bagasse fiber/recycled polypropylene nanocomposites. FTIR spectra indicated the reduction of bagasse fibers’ hydroxyl moieties due to hemicellulose removal resulting from alkali treatment. There were also trace diminutions in C-O peak intensities due to the degradation of little amounts of lignin. X-ray Scattering revealed the intercalation of nanoclay in the polymer matrix. The improved interaction of fiber-polymer interfaces brought about by alkali treatment was also confirmed by scanning electron microscopy. The physical properties of the nanocomposites were improved due to the barrier properties of nanoclay against water ingress. The flexural strength and modulus of elasticity increased by both individual and combined treatments; however, the impact strength decreased by the individual treatments. Thermogravimetric analysis demonstrated that the temperatures of first and second stages of composites’ thermal degradation increased due to the treatments via the formation of a carbonized char layer thermally insulating the deeper composite layers. Differential scanning calorimetry showed some slight increases in the melting temperature, melting enthalpy, crystallisation temperature, crystallisation enthalpy, and crystallinity index of the treated composite formulations due to the nucleating effect of nanofillers. The overall results confirmed that the combination of nanoclay cloisite 20A and NaOH treatments could significantly improve the overall properties of the studied composites. This was due to some interesting synergistic effects of the given treatments on the nanocomposites converting the bagasse/recycled PP composites to high performance materials of choice.

Impact modification of wood flour reinforced PP composites: Problems, analysis, solution

Impact modification of wood flour reinforced PP composites: Problems, analysis, solution

Influence of injection molding parameters, melt flow rate, and reinforcing material on the weld‐line characteristics of polypropylene

AbstractIn this work, the relation of injection molding parameters to the mechanical properties of various polypropylene grades is investigated to find the optimal processing parameters to minimize weld‐line effects like reduced mechanical and/or optical performance. Injection molded test specimens of five polypropylene grades with different melt flow rates were characterized for their mechanical behavior and compared with equal‐shaped specimens with a colliding weld line in the middle of the specimen. For the production of these weld‐line specimens, a special mold was used and injection molding parameters were systematically varied, tensile (ISO 527‐2) and impact (ISO 179‐1/1eU) properties were measured, and statistical analyses were performed to gain insight on the correlation between melt flow rate and weld‐line behavior. It showed that mechanical properties of specimens with weld lines can be influenced by the processing parameters, but the effect is limited. Positive correlations were found between tool temperature and tensile modulus and strength. Polypropylene grades with low melt flow indexes seem to be more susceptible to weld‐line‐induced property reductions. In a second test series similar to the pure PP investigations, glass‐fiber‐ and talc‐filled PP were used to gain insight into the weld‐line behavior of PP composites. In addition to mechanical characterization, optical and scanning electron micrographs were taken of the weld‐line areas. It was found that the reinforcing particles align along the melt flow front in the weld‐line area. As a result, the mechanical performance of weld‐line specimens is poor. Injection molding parameters were found to have only a small effect.

Smoke suppression, flame retardancy, and fire toxicity of polypropylene containing melamine salt of pentaerythritol phosphate halloysite

AbstractPolypropylene (PP) was melt blended with a new mono molecular intumescent flame retardant, melamine salt of pentaerythritol phosphate halloysite (MPPH) to enhance its thermal stability, flame retardancy, and smoke suppression properties. The structure of MPPH was elucidated by Fourier transform infrared (FTIR), 1H NMR, X‐ray diffraction (XRD), and energy dispersive X‐ray (EDX) analysis. PP composites results showed that MPPH increased the thermal stability of PP at high temperatures in all PP composites. The horizontal flammability test (UL94H) showed that MPPH stopped flame propagation in PP composites. Vertical burning rate test (UL94V) revealed that PP composites can attain V0 rating at loading levels 25, 30, and 35 wt.% of MPPH. Limiting oxygen index (LOI) data indicated that adding 20, 25, 30, and 35 wt.% of MPPH to PP increased the LOI value of PP (19.2%) to 27.1%, 32.5%, 35.4%, and 38.7%. MPPH succeeded in reducing the maximum specific optical density (Dsmax), mass specific optical density (MOD), and rate of smoke generation during the first 4 min (VOF4) of PP composites compared to PP alone. FTIR gas analyzer results revealed that MPPH decreased the emission of CO and CO2 in the gas phase during the combustion process. Digital photos and scanning electron microscope (SEM) images of char residues remained after the smoke density test revealed that MPPH succeeded in forming a cellular and cohesive char layer on the PP surface. The new data is expected to increase the use of PP in rigid packaging applications.

Mechanical and Thermo-Mechanical Performance of Natural Fiber-Based Single-Ply and 2-Ply Woven Prepregs.

This paper presents a study conducted on prepregs manufactured by a novel method for the impregnation of a thermoplastic matrix. Different composite prepregs based on polypropylene and reinforced with natural fibers (e.g., basalt and jute fibers) were developed. The mechanical and dynamic mechanical properties were investigated. DMA tests were conducted at 1 Hz frequency and properties such as storage modulus and damping (tan δ) were evaluated. The overall mechanical properties of the basalt fiber composites were found to be superior to that of the jute fiber-based samples. Thermo-gravimetric analysis (TG/DTG) of the composite samples showed that the thermal degradation temperatures of the basalt-based composites shifted to higher temperature regions compared to the PP or jute fiber composites. The addition of basalt fiber considerably improved the thermal stability of the composite samples. Microscopic images of the tensile fractured composite samples illustrated better fiber-matrix interfacial interaction due to the novel technology of prepregs. Single-ply and 2-ply prepregs showed significantly superior mechanical, thermal, and thermo-dynamical performance compared to the control sample (pure PP). 2-Ply composites demonstrated higher modulus, tensile strength, and storage modulus due to the higher fiber volume fraction. Basalt-based samples showed a minimum weight loss of about 57% up to 700 °C in contrast to 96.05% weight loss in the jute-based samples and 98.4% in the case of pure PP. The heat resistance index (THRI) is more than twice for basalt compared to jute and PP. Furthermore, the superior thermal stability of basalt is reflected in its DSC curves, showing the highest endothermic peak. The technique of using the resin in the form of thermoplastic yarns offers cost effective and efficient alternatives for composite manufacturing.

Effect of alkylated surface modified silica nanoparticles on degradation products of PP during photooxidation aging: A Py-GC-MS analysis

Introducing nano-fillers to PP matrix improves its mechanical performance, but impairs the stability and changes its aging behavior. Surface modification of nano-fillers may have further influence. To investigate the effect of alkylated surface modified silica nanoparticles on PP degradation during photooxidation aging, Py-GC-MS flash evaporation technique was applied to qualitatively analyze the degradation products and quantitatively analyze their accumulation during photooxidation aging. Thermal processing of PP composites led to thermal decomposition and oxidation before aging. During photooxidation aging, both silica nanoparticles and the alkylated surface modification promoted the oxidative degradation of PP. Oxidation products accumulated, while the aging mechanism did not change. Nine typical oxidation products with different carbon numbers were selected and their accumulation during photooxidation aging were analyzed. For C1-C6 total oxidation products, there exhibits an induction period and subsequent linear accumulation during photooxidation aging. The induction period was used to show the effect of nano-silica and its surface modification. It was shortened by introducing nano-silica and further shortened by alkylated surface modification of nano-silica.

Development of polypropylene-based composites through fused filament fabrication: The effect of carbon-based fillers

• PP composites reinforced with carbonaceous fillers were developed using FFF. • Filaments of each material were processed, and a viable FFF process was optimized. • The effect of fillers was evaluated in terms of materials' thermo-physical properties. • The addition of fillers led to improvements of mechanical properties of FFF samples. Fused Filament Fabrication (FFF) is the most widespread additive manufacturing technique for polymeric materials. However, only a limited number of materials are available to be processed through this technique. Polypropylene and its composites are extremely versatile materials which are employed in a wide range of applications, but their use in FFF has not been much investigated due to issues related to adhesion and warping. In this work, composites having polypropylene as matrix and different carbonaceous fillers, namely carbon nanotubes and carbon fibers, were developed using FFF. Compounding, filament extrusion and FFF processes were successfully developed and optimized for each material. The materials were characterized in terms of their thermo-physical properties and the effect of the fillers on these properties was investigated. The addition of carbon fibers led to a significant improvement of mechanical properties, and a more moderate increase was observed in the case of carbon nanotubes addition.

High improvement of interfacial and mechanical properties in reinforcedPPcomposite by grafting polyethyleneimine modified carboxylicmulti‐walledcarbon nanotubes on short carbon fiber

AbstractThe properties of carbon fiber reinforced polymer composites (CFRPs) will benefit greatly from improving interfacial performance. In this study, the interfacial properties of the PEI‐CNT‐CF/PP composite was improved by coating polyethyleneimine (PEI) modified carboxylic multi‐walled carbon nanotubes (CNTs) in aqueous solution (PEI‐CNT) onto the surface of the CF (PEI‐CNT‐CF) to form a network structure. The network formation changed the chemical characteristics and compatibility of CF surface by introducing amine (imine) groups, and could induce transcrystallization (TC) at interface of composite. These positive factors led to a 24.6% increasement in the interfacial shear strength (IFSS) of PEI‐CNT‐CF/PP, and further resulted in 16.2% and 5.3% improvement in tensile and flexural strength, respectively. SEM images of the fracture surface demonstrated a significant improvement in the interfacial adhesion between PEI‐CNT‐CF and PP resin. These results indicated that the PEI‐CNT was a great choice to strengthen the interface of CF/PP system.

Synergistic flame retardancy of ZnO with piperazine pyrophosphate/melamine polyphosphate in PP

Common ZnO particles was used to improve the flame retardancy of piperazine pyrophosphate/melamine polyphosphate (PPAP/MPP) in PP composites. 0.5 wt% ZnO exhibited an exceptional synergism by analyzing LOI determination, UL-94 test, and CCT. The LOI increased from 29.9% (no ZnO) to 32.3%. The corresponding flame-retardant rating was improved from UL-94 V-2 to V-0. Additionally, ZnO significantly inhibited the formation of the smoke and CO during the combustion process. The TGA, the component and the structure of the heated FRPP and CCT residues were studied by FTIR, EDS, SEM, Raman spectra and 31P Nuclear Magnetic Resonance, revealing that PPAP/MPP was dominant in the flame retardant process by condensed phase actions. Furthermore, ZnO obviously promoted the formation of the char layer and increased its graphitization degree. Thus, the thermal stability and the strength of the intumescent char layer were improved and then to reinforce the flame retardancy of flame retardant PP (FRPP).

Enhancement of mechanical properties of high modulus polypropylene grade for multilayer sewage pipes applications

AbstractAdvances in technology have provided fresh generations of stiff polypropylene block copolymers for gravity sewerage applications. The aim of this study is to further enhance the stiffness of these materials through the incorporation of inorganic fillers. In this study, three talc filled PP and one glass fiber filled PP composites were characterized in order to be used as a middle layer in a three‐layer sewage pipe. The obtained results showed an increase of approximately more than 100% and 250% in tensile and flexural moduli by the use of 30%–50 wt% talc‐filled PP and 30 wt.% glass fiber‐filled PP, respectively. This high increase in the rigidity of the material would allow manufacturing pipes with improving ring stiffness. Composites filled with 30 wt% talc or glass fiber showed good filler‐matrix interaction and good filler distribution and dispersion. However, reduced filler‐matrix interaction was observed in the case of the composite filled with 50 wt% talc. In addition, the use of Differential Scanning Calorimetry analysis revealed that the addition of fillers enhanced the crystallization temperature of the polypropylene matrix. Furthermore, Thermogravimetric Analysis showed that the high modulus PP grade retained its thermal stability in the various composites.

In situ formation of core‐shell rubber particles in polypropylene matrix by melt blending and its effects on the toughness and stiffness of the composites

AbstractToughening of thermoplastics with a one‐phase impact modifier generally results in significant reduction in stiffness, whereas core‐shell rubber modifiers have extra structural parameters such as core rigidity and shell flexibility, by controlling which the stiffness and impact toughness of their composites can be better balanced. In this study, three kinds of polyethylene (PE) with different rigidity are used respectively to prepare polypropylene/ethylene–propylene rubber/polyethylene (PP/EPR/PE) ternary composites by melt blending, in which the EPR‐to‐PE ratio is 1:1. Atomic force microscopy‐infrared (AFM−IR) and scanning electron microscopy (SEM) results indicate that core‐shell rubber particles with a PE core and an EPR shell are formed in situ and uniformly dispersed in the PP matrix. Mechanical measurements show that at the same modifier content the PP composites toughened with these core‐shell rubber particles exhibit higher toughness and stiffness than that with EPR alone, and the more rigid the PE core, the greater the effects. These results are in quantitative agreement with a recent theoretical model, providing solid experimental evidence in support of the latter. Furthermore, this work demonstrates an economical approach to toughening PP by partial substitution of the EPR with the much cheaper PE for better performance.

Gradient characteristics of crystal, chemical structure, and nanoscale mechanical properties in the transcrystallinity of bamboo fiber anchored nano-TiO2/PP composites

Gradient characteristics of crystal, chemical structure, and nanoscale mechanical properties in the transcrystallinity of bamboo fiber anchored nano-TiO2/PP composites

Synergistic flame retardancy of ZnO and piperazine pyrophosphate/melamine cyanurate in polypropylene

AbstractIn order to improve the flame retardant efficiency and smoke‐suppression of piperazine pyrophosphate/melamine cyanurate (PPAP/MCA) in PP, the synergism of ZnO and PPAP/MCA was investigated by limiting oxygen index (LOI) determination, UL‐94 test, and cone calorimetry test (CCT). It is found that ZnO performs an exceptional synergism in flame retardant effect and inhibition on the flame propagation. Besides, ZnO can significantly inhibit the production of the smoke and CO. The TGA of the PP composites, the component and structure analysis of the heated composites and CCT residues reveal that ZnO performs the synergism primarily by the following modes: ZnO promotes obviously the charring of the composite, and improves the thermal stability as well as the strength of the intumescent layer, which brings about an improved flame retardant property and inhibiting ability on the flame propagation.

The piperazine pyrophosphate intumescent flame retardant of polypropylene composites prepared by selective laser sintering

AbstractA highly flame‐retardant PP composite powder suitable for selective laser sintering (SLS) was prepared successfully by mechanical blending, which was composed of pure PP, piperazine pyrophosphate (PPAP), melamine polyphosphate (MPP), and triazine‐based charring‐foaming agent (CFA). The results showed that the flowability of PP composite powder decreased by about 40% and the DSC data indicated the sintering window decreased by about 2°C. Although the flame retardants influenced the processing of SLS, the PP composite powder was still able to be used for printing. The LOI value of PP composites prepared by SLS was 29.2% and the UL‐94 grade was V‐0 rating at the filler loading (16wt% PPAP, 4wt% MPP, 4wt% CFA). The cone calorimeter testing (CCT) data represented that the heat and smoke release significantly decreased. The synergistic effect among flame retardants promoted high‐quality char layers, which is favorable for improving the flame retardancy and thermal stability of PP composites by the test of TGA, SEM, Raman spectra, and FT‐IR. However, the flame retardancy and mechanical properties of PP composites made by SLS were both in varying degrees of decline compared to the ones made by thermo‐compression (TC) because of the higher porosity. An air duct with complex structures was prepared by SLS at last.

Ultrahigh Low-Temperature Toughness of Polypropylene Composites with Low Ductile-Brittle Transition Temperature by Introducing Traces of Needlelike Wollastonite

In order to survive harsh settings, such as outer space, deep sea and high plains, needlelike wollastonite fibers (WF) were incorporated into polypropylene/ethylene octene block copolymer/β-nucleating agent (PP/OBC/β-NA) blends with the hope of tailoring the low-temperature toughness. The results revealed that WF showed very satisfactory toughening effects in the PP/OBC/β-NA/WF composites at low temperature (–20 °C). The impact strength of the WF-0.05 was as high as 32.1 kJ/m2 at −20 °C, which was 286.6% higher than that of the WF-0 sample, and even 832.6% higher than that of the pure PP sample. SEM characterization showed that by simultaneously adding WF and β-NAs, much coarse and tremendous plastic deformation appeared in the WF-0.05 after impacting. The low-temperature toughening mechanism is systematically discussed. The increase of β-crystallinity, caused by the synergy of β-nucleating agent and WF fillers, was mainly responsible for the enhancement of the impact strength of the composites with WF. On the other hand, when the transmitting of the stress, the overlapping of the stress and the hindering effect of WF on cracks occurred simultaneously; it resulted in the excellent low temperature toughness of the PP composites. Such outstanding-performance material with the advantages of facile processing and low cost is unprecedented. It shows a promising future application in many fields, especially aerospace, navigation, and the automotive industry.

Bio-Based Composites for Light Automotive Parts: Statistical Analysis of Mechanical Properties; Effect of Matrix and Alkali Treatment in Sisal Fibers.

Composites based on virgin and recycled polypropylene (PP and rPP) reinforced with 15 wt% sisal fibers, with and without alkali treatment, were prepared by compression molding in a mat composed of a three-layer sandwich structure. The sisal was characterized by Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The composites were characterized according to physical and mechanical properties. Additionally, a factorial experimental design was used to statistically evaluate the mechanical properties of the composite. The FTIR and XRD indicated the partial removal of amorphous materials from the surface of the sisal after alkali treatment. The composites’ density results varied from 0.892 to 0.927 g·cm−3, which was in the desirable range for producing lightweight automotive components. A slight decrease in the hardness of the pure rPP and rPP composites in relation to the PP was observed. The water absorption was higher in rPP composites, regardless of the chemical treatment. Moreover, the impact resistance of PP and its composites was higher than the values for rPP. Statistical analysis showed that the alkali treatment was a significant factor for the hardness of the rPP and PP composites, and that the addition of the sisal layer was relevant to improve the impact resistance of the composites.

Characterization of Biodegradable Composites from Polypropylene, Polypropylene Grafted Maleic Anhydride, and Durian Seed Starch

The characterization of biodegradable composite from durian seed starch that is mixed polypropylene, and polypropylene grafted maleic anhydride has been done. The stages of this preparation were, the first had prepared durian seed starch, the second had the process of grafting maleic anhydride into polypropylene and the third had made of composite with the composition of PP:PP-g-MA: DSS (7:0.5:0.2); (7:0.5:0.3); (7:0.5:0.4); (7:0.5:0.5); (7:0.5:0.6) (w/w). The biodegradable composites obtained were characterized by tensile strength, surface morphology analysis by SEM, differential thermal analysis (DTA), analysis in nature with the ability to decompose biodegradable test, and functional groups analysis by FTIR spectroscopy. The results showed that the biodegradable composites have the best properties in the ratio of PP:PP-g-MA: DSS was (7:0.5:0.5) (w/w) with the test results of tensile stress is 12.556 N/m2, and the elongation is 8.600%, the images on a few flat surfaces and improved homogeneity, temperature change, and strong group interactions as well as having good biodegradable properties.

Synthesis of a charring agent containing triazine and benzene groups and its intumescent flame retardant performance for polypropylene

A novel linear triazine-based charring agent, N-Ethanolamine Triazine-4,4-diaminodiphenylsulfone-piperazine copolymer hybrids (ETDPCs), was successfully synthesized and was combined with fire-retardant (FR) (mass ratio 2:1 of ammonium polyphosphate (APP) and melamine pyrophosphate (MPP)) to fabricate intumescent flame-retard PP composites at a 20 wt% loading, which exhibited excellent char-forming capacity and thermostability. The value of the limiting oxygen index (LOI) reached 30.4% and the vertical burning test (UL-94) passed V-0 grade for the PP2 sample with a mass ratio of FR to ETDPCs being 3:1. The cone calorimeter test revealed that the total heat release (THR) and total smoke release (TSR) of PP2 were significantly decreased by 61.8% and 87.9% compared with that of pure PP. The flame retardancy index (FRI) of PP2 was 12.2, showing an “Excellent” grade of flame retardancy. The thermogravimetric results showed that ETDPCs presented good char formation ability, and it would greatly increase the charring yield of PP when combined with FR due to the synergistic effect. The investigation of the structures and properties of char residues indicated that the continuous and compact char layer with high mechanical stability and low thermal conductivity, containing benzene and triazine derivatives, was formed for PP2 during combustion, which acted as a good barrier against the transmission of heat and volatiles and movement of high-temperature melt. This work expanded the avenue in the synthesis of high-efficiency charring agents and improved the intumescent flame retardancy of PP.

Recycling of municipal sewage sludge incineration fly ash based on (NH4) 2SO4 roasting-acid leaching and filling PP matrix process.

Sludge incineration is one of the most efficient sludge treatment methods. The fly ash produced by incineration must be handled further since it has a significant number of heavy metals. In this study, the chemical composition of sewage sludge incineration fly ash (SSA) generated from Zhejiang in various months was identified by XRD, X-ray fluorescence spectrometer (XRF), and SEM analyzes. The SSA were treated by a (NH4)2SO4 roasting-acid leaching process to determine its effect on the elimination performance of heavy metals. The SSA content on the mechanical properties and heavy metal leaching of modified SSA-filled PP composite were also studied. Results show (NH4)2SO4 roasting-acid leaching process has a good effect of eliminating heavy metals, with the highest leaching of Zn of 86.4%. The presence of sodium stearate modifier increases activation index of SSA and then improves the compatibility of SSA particles in PP, resulting for the composites have relatively excellent mechanical properties. For the toxicity characteristic leaching procedure (TCLP) test, modified SSA particles can be effectively encapsulated with PP resins, which have a considerable inhibitory effect on heavy metal leaching. This process from this study provides a reference for sewage sludge treatment by using modified SSA as a polymer filler to achieve the immobilization of heavy metals and the resource recycling.

Mechanical Properties of Bambusa Oldhamii and Yushania-Alpina Bamboo Fibres Reinforced Polypropylene Composites.

The current studies aim to measure the mechanical strength based on age, harvesting season and bamboo species in Ethiopia. The bamboo fibres are extracted using a roll milling machine, which was developed by the author. The age groups (1, 2 and 3 years), harvesting months (February and November), and bamboo species (Yushania alpina and Bambusa oldhamii) are the parameters of the current research studies. Prepregs and composites were produced from bamboo fibres and polypropylene. The mechanical properties of bamboo fibres and their composites in Ethiopia have not been investigated by researchers for the composite application so far. The tensile strength, Young’s modulus, and impact strength of injibara (Y. alpina) bamboo fibres reinforced PP composites from the ages of 1– 3 years old in November is 111 ± 9–125 ± 8 MPa, 15 ± 0.9–25 ± 0.72 GPa, and 47 ± 5 KJ/m2–57 ± 6 KJ/m2, whereas, in February, it is 86 ± 3.86–116 ± 10 MPa, 11 ± 0.71–23 ± 1.5 GPa, and 34 ± 4–52 ± 6 KJ/m2, respectively. Moreover, Kombolcha (B. oldhamii), bamboo fibres reinforced PP composites in November are 93 ± 7–111 ± 8 MPa, 7 ± 0.51–17 ± 2.56 GPa, and 39 ± 4–44 ± 5 KJ/m2, whereas, in February, it is 60 ± 5–104 ± 10 MPa, 12 ± 0.95–14 ± 0.92 GPa, and 26 ± 3 KJ/m2–38 ± 4 KJ/m2, respectively. Furthermore, Mekaneselam (Y. alpina) bamboo fibres reinforced PP composites in November are 99 ± 8–120 ± 11 MPa, 9 ± 0.82–16 ± 1.85 GPa, and 37 ± 4 KJ/m2–46 ± 5 KJ/m2, whereas, in February, it is 91 ± 8–110 ± 9 MPa, 8 ± 0.75–14 ± 1.86 GPa, and 34 ± 3 KJ/m2–40 ± 4 KJ/m2, respectively. At two years, November and Injibara bamboo have recorded the highest mechanical properties in the current research studies. Bamboo fiber strength in Ethiopia is comparable to the previous study of bamboo fibres and glass fibres used for composite materials in the automotive industry.