Properties Of Polypropylene Composites Research Articles

Multi‐objective optimization of hybrid polypropylene composites for enhanced mechanical, thermal, and flame‐retardant properties

AbstractOptimizing composite materials is crucial for engineering advancements because it allows for the creation of materials tailored to specific functional requirements, thereby enhancing efficiency, safety, and sustainability. This study examines both the combined and individual effects of long flax fiber (LFF) bundles, short basalt fibers (BF), and rice husk powder (RHP) on the properties of polypropylene (PP) hybrid composites. LFF primarily provides mechanical strength, BF enhances mechanical, thermal, and flame‐retardant properties by filling gaps, and RHP reinforces and improves the overall composite. Contrary to previous studies that relied on random combinations, this research employs a systematic Box–Behnken design (BBD) for three variables: LFF plies, BF, and RHP by weight percentage. This approach facilitated the development of a new second‐order regression equation via response surface methodology (RSM), clarifying the contribution of each component, with R2 values exceeding 0.85, indicating high predictability. Optimization, conducted using a non‐dominated sorting genetic algorithm (NSGA‐II), demonstrated that the optimal composites significantly outperformed the non‐optimized ones in mechanical strength, thermal stability, and flame retardancy. Compared to the average values before optimization, improvements post‐optimization included increases of 49.86% in tensile strength (TS), 38.82% in TS modulus, 73.93% in char yield (YC), and 29.81% in peak heat release rate (pHRR). Specifically, the fire performance index improved by 237.5% and the fire growth index by 101.33%, compared to pure PP, highlighting significant advancements in fire safety. This study shows that mathematical equations can predict composite properties, helping to select balanced compositions without sacrificing flammability.Highlights Multi‐filler approach technique used for manufacturing of PP composites. LFF, BF & RHP optimize mechanics & flammability. Box–Behnken design predicts optimal composition for superior properties. NSGA‐II optimization improves tensile, thermal & flame retardant properties.

The Effect of Thermoplastic Elastomer and Fly Ash on the Properties of Polypropylene Composites with Long Glass Fibers.

A cost-effective solution to the problems that the automotive industry is facing nowadays regarding regulations on emissions and fuel efficiency is to achieve weight reduction of automobile parts. Glass fiber-reinforced polymers are regularly used to manufacture various components, and some parts may also contain thermoplastic elastomers for toughness improvement. This work aimed to investigate the effect of styrene-(ethylene-co-butylene)-styrene triblock copolymer (E) and treated fly ash (C) on the morphological, thermal, and mechanical properties of long glass fiber (G)-reinforced polypropylene (PP). Results showed that the composites obtained through melt processing methods presented similar thermal stability and improved (nano)mechanical properties compared to 25-30 wt.% G-reinforced PP composites (PP-25G/PP-30G). Specifically, the impact strength and surface hardness were greatly improved. The addition of 20 wt.% E led to a 25-39% increase in impact strength and surface elasticity, while the addition of 6.5 wt.% C led to a 16% increase in surface hardness. The composite based on 25 wt.% G, 6.5 wt.% C, and 20 wt.% E presented the best-balanced properties (8-17% increase in impact strength, 38-41% increase in axial strain, and 35% increase in surface hardness) compared with PP-30G/PP-25G. Structural and morphological analysis confirmed the presence of a strong interaction between the components that make the composites. Based on these results, the PP-G-E-C composites could be presented as a viable material for automotive applications.

Preparation of high-performance anti-aging polypropylene by modified nano-TiO2 and calcium sulfate whisker grafted acrylonitrile composite PP.

By employing the radical polymerization method, acrylonitrile (AN) was grafted on the surface of nano titanium dioxide (TiO2), and the calcium sulfate whisker (CSW) was modified using the coupling agent KH570 to provide ultraviolet (UV)-absorption capacity. The prepared TiO2-PAN and CSW-PAN materials can improve the anti-aging performance and mechanical properties of polypropylene (PP) and meet the application requirements of high-performance polypropylene. Further, the obtained PP composites show prolonged service life and application scope, which can effectively reduce white waste and avoid both resource waste and environmental pollution.

Surface Roughening of Irradiation-Activated Basalt Fiber through In Situ Growth of SiO2: Effects on Crystallization and Properties of PP Composites.

Basalt fiber (BF) is deemed a new environmentally friendly and high-performance fiber material due to its high strength, electrical insulation, corrosion resistance and high temperature resistance. Yet, the surface inertness restricts its practical application. In this work, the BF was irradiated and activated by electron beam, followed by in situ growth of SiO2 using a hydrothermal method, then composites with polypropylene (PP) were prepared by microinjection molding. According to the results of scanning electron microscopy (SEM) and Fourier transform infrared (FTIR), more active sites can be formed after irradiation, thus more SiO2 nanoparticles were generated on the surface of BF. Consequently, the rough surface of modified BF could provide stronger shear force during melt processing and resulted in a higher orientation of the molecular chains, increasing the lamellar thickness and generating more highly ordered β crystals in the composites. I400BF-gSiO2 exhibited the highest content of β crystals with the crystallinity of 53.62% and orientation of β (300) crystal plane of 0.91, which were 8.66% and 0.04 higher than those of the composite with pristine BF. Furthermore, due to the perfection of crystals, increased interfaces and interfacial interlocking between PP molecules and modified BF, I400BF-gSiO2 showed good overall performance, with storage modulus of 8000 MPa at -100 °C, glass transition temperature of 23.03 °C and tensile strength of 62.2 MPa, which was 1900 MPa, 1.23 °C and 29.6 MPa higher than neat PP. Hence, the surface roughing strategy proposed in this work is expected to provide some insight and promote the application of BF reinforced thermoplastic composites.

Machine learning-based heat deflection temperature prediction and effect analysis in polypropylene composites using catboost and shapley additive explanations

Among the various physical properties of polypropylene composites (PPCs), heat deflection temperature (HDT) during PPC production is significant because it is directly related to the mechanical behavior of such products. However, it is difficult to predict and analyze the HDT of PPCs owing to the absence of a mathematical or theoretical model. Moreover, categorical data which has different physical properties despite using same substances made predictions highly difficult in PPCs. Here, this study proposed an indicator to analyze the categorical data and Catboost-based model for HDT prediction considering the categorical data. First, the categorization and minimum-based values (MBVs), a dimensionless factor used to calculate HDT differences in the categorical dataset, are applied to detect and split categorical data in a PPC dataset. Second, a case study was conducted on the dataset using three algorithms to compare the proposed model with other traditional machine-learning approaches. As a result, the proposed model provides the highest prediction performance of R2=0.8965 and 0.9801, for the total test dataset and the categorical dataset, respectively. In addition, the effect analysis of substances on HDT was conducted to get some prospective substances for the required HDT using Shapley Additive Explanations (SHAP). Thus, the results of this study can provide a guidance for selecting prospective substances using SHAP result for the target HDT and adjusting the substance ratio using the proposed model. It is expected that this framework has the potential for being applied to the other blending processes to produce products with the required properties.

Characterization of Thermo-Mechanical and Chemical Properties of Polypropylene/Hemp Fiber Biocomposites: Impact of Maleic Anhydride Compatibilizer and Fiber Content.

This article presents a comprehensive study on the physical, mechanical, thermal, and chemical properties of polypropylene (PP) composites reinforced with hemp fibers (HF) and compatibilized with maleic anhydride (MAPP). The composites were processed using a twin-screw extruder, followed by hot compression at 190 °C. Subsequently, the composites were analyzed using Izod impact and Shore D hardness tests to evaluate their mechanical properties. Thermal properties were investigated through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), while X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) were employed to study their chemical properties. Additionally, a statistical analysis was conducted to compare the average results of the impact and hardness tests. XRD analysis revealed that the addition of HF and MAPP led to the disappearance of peaks corresponding to the beta phase in pure PP. Hemp fibers exhibited an impressive crystallinity of 82.10%, surpassing other natural fibers, and had a significant molecular orientation angle (MFA) of 6.06°, making them highly desirable for engineering applications. The crystallite size was observed to be relatively large, at 32.49 nm. FTIR analysis demonstrated strong interactions between the fiber, compatibilizing agent, and polymer matrix. TGA tests showed that the addition of 5 and 10 wt.% MAPP resulted in complete degradation of the composites, similar to pure PP. DSC analyses indicated a reduction in crystallinity (Xc) due to the incorporation of HF and MAPP. Shore D hardness tests revealed an increase in hardness with the addition of 5 wt.% MAPP, while a steep decline in this property was observed with 10 wt.% MAPP. In terms of impact resistance, fractions of 3 and 5 wt.% MAPP in the composites exhibited improved performance compared to the pure polymer. Analysis of variance (ANOVA) was employed to ensure the statistical reliability of the mechanical test results. This comprehensive study sheds light on the diverse properties of PP composites reinforced with hemp fibers and compatibilized with MAPP, emphasizing their potential as sustainable materials for engineering applications. The results contribute to the understanding of the structural and functional aspects of these composites, guiding future research and developments in the field.

Toughening behavior and synergistic flame retardant effect of a ternary block copolymer with amorphous morphology and thermal softening property in polypropylene

A novel intumescent flame retardant with ternary block copolymer style not only more effectively enhanced flame retardant efficiency but also dramatically increased mechanical properties of polypropylene (PP) composites compared with traditional compounds. The ternary block copolymers were synthesized by the dehydration reaction of polydiphenylsiloxane, piperazine pyrophosphate oligomer and melamine phosphate. Among them, the ternary block copolymer T4-0.8PSi with particular unit ratio presented best comprehensive effect in PP composites. The LOI value of PP composite T4-0.8PSi/PP with 20 wt% T4-0.8PSi reached 30.2 %, and UL94 level of 1.6 mm spline passed V-0 rating. Compared with binary block copolymer B1 and the mixtures B1/0.8PSi and Mix/0.8PSi with similar contents as T4-0.8PSi, T4-0.8PSi obviously reduced the peak value of heat release rate, total heat release, effective heat of combustion and total smoke release. Particularly, it dramatically increased the residue yield and promoted the formation of denser and compact char layer. The ternary block copolymer T4-0.8PSi with appropriate group ratio generated synergistic charring effect in PP. At the same time, the mechanical properties of T4-0.8PSi/PP were dramatically enhanced and the impact strength was increased by 14.5 % compared with B1. Compared with the two mixtures just mentioned, the impact strength of T4-0.8PSi/PP increased by 48.8 % and 103.3 %, and the elongation at break increased by 601 % and 2056 %, respectively. The silicon-containing unit in ternary block copolymer nearly eliminated crystallinity to form amorphous morphology, which made flame retardants deform to droplet-like particles during processing, thus resulting in the more contact area and stronger interaction between the ternary block copolymer and polymer matrix. The research provided a new way for developing polyolefin materials with both high flame retardancy and excellent mechanical properties.

Effect of Hollow Glass Microspheres with Different Contents and Types on Properties of Polypropylene Composites

AbstractIn this paper, hollow glass microspheres (HGM) reinforced polypropylene (PP) composites were prepared. The effects of the type and content of HGM on the mechanical properties of the composite materials were investigated. It is found that the introduction of HGM leads to a decrease in the density of the composites, where the smallest density is 0.85 g cm−3. The tensile, bending, and impact strengths of the HGM/PP composites are slightly lower than those of pure PP resin. For a given type of HGM, as the filler content increases, the tensile properties of the HGM/PP composite decrease. A similar trend is observed in the impact strength, however, it is not observed in the bending performance. The mechanical properties of the HGM/PP composites are not only affected by the density of HGM fillers, but also by its content. The maximum bending modulus of the composites could be 24 % higher than that of the pure PP resins. In addition, the PP sample with HGM modified with γ‐aminopropyl triethoxysilane (KH550) showed promising interfacial bonding strength.

Effect of polymer type on the properties of polypropylene composites with high loads of spent coffee grounds

The main focus of this work is to study the processability and characteristics of highly loaded spent coffee grounds (SCG) thermoplastic polymer composites, for sustainable applications. SCG powder was characterized in terms of size distribution, moisture, morphology and thermal stability. Polymer/SCG composites were prepared by extrusion compounding. Polypropylene (PP) homopolymer and copolymer were used as the polymeric matrix. Upon compounding by extrusion composites were injection moulded and characterized for its physical, morphological and mechanical properties in order to determine the effect of polymer type and filler content. Morphological characteristics of the composites were investigated using optical microscopy and SEM analysis. The results for PP homopolymer showed little deterioration of the mechanical properties when using the highest SCG load. In the case of PP homopolymer, the greatest variations occurred when increasing from 0 to 20 %. With higher SCG loads, the measured properties changed little. PP copolymer showed a more continuous pattern of properties decay with increasing SCG load, especially for tensile strength, elongation at break and impact strength. Regarding PP copolymer, with maximum SCG load, the tensile strength decreased from 26.8 GPa (neat PP) to 10.8 GPa, the elongation at break showed a drop of more than 95 %, while the Young’s modulus increased from 800 MPa to 1160 MPa. This research work has shown that SCG can be used as fillers in the preparation of environmentally friendly composites with SCG load up to 60 wt% thus contributing to the reuse of waste generated by the coffee industry.

Fabrication and Mechanical Properties of High-Durability Polypropylene Composites via Reutilization of SiO2 In-Situ-Synthesized Waste Printed Circuit Board Powder.

This paper focuses on the characterization of the physico-chemical properties, surface modification, residual copper content and in situ hybrid inorganic particle modification of polypropylene (PP) composites reinforced by waste printed circuit board powder (WPCBP). A series of WPCBP/SiO2 hybrids (TSW) were prepared by a sol–gel method at different pH values. Characterization results revealed the in situ generation of SiO2 on the surface of WPCBP, and showed that with an increase in pH value, the size of SiO2 particles increased gradually and the copper content decreased in the TSW powder. The mechanical properties, oxidation induction time (OIT) and thermal properties of PP composites were improved by reinforcement with TSW, which might be ascribed to the formation of serrated interfaces. This work not only develops a powerful method to enhance the properties of PP/WPCBP composites, but also provides an environmentally sustainable approach to the high-added-value reutilization of WPCBP.

Improving antistatic and mechanical properties of glass fiber reinforced polypropylene composites through polar adsorption and anchoring effect of organic salt

Matrix toughness and viscosity, fiber length, interface bonding, and crystalline structure play significant roles in tuning the antistatic and mechanical properties of polypropylene (PP) composites. However, there is no report available concerning the development of antistatic PP composites by considering all these factors. In this study, we fabricate antistatic long glass fiber reinforced polypropylene random copolymer composites filled with Li-TFSI (LGF/PPR/Li-TFSI) and explore how crystallization behavior due to Li-TFSI affects the interfacial strength and conductive mechanism. It is found that the polar effect promotes the adsorption of Li-TFSI on the surface of LGF to form a conductive track, and consequently, the three-dimensional conductive network formed by intertwined LGF effectively reduces the percolation threshold (i.e., 0.15 wt/wt%). Besides, the heterogeneous nucleation induced by Li-TFSI promotes the nucleation and crystal growth of PPR molecular chains on the surface of Li-TFS. Thus, Li-TFSI wrapped by spherulites improves the anchoring effect of the LGF on the PPR matrix. However, the anchorage degree is related to the close proximity of conductive particles, specifically, 0.05 wt/wt% Li-TFSI results in the highest level of stress transfer. Meanwhile, although the addition of 0.15 wt/wt% Li-TFSI causes a slight decrease in the interface strength, it leads to competitive nucleation between Li-TFSI and LGF, thereby generating thicker lamellae, which makes LGF/PPR/Li-TFSI the largest modulus. This study provides some new insights into the tailoring of material properties using Li-TFSI for antistatic PP composites.

Synthesis of ß-strontium hydrogen phosphate nanosheets and its effect on thermal and tribo-mechanical properties of polypropylene composites

Synthesis of ß-strontium hydrogen phosphate nanosheets and its effect on thermal and tribo-mechanical properties of polypropylene composites

Effect of a new amido‐imidazolium compound as a clay modifier on properties of polypropylene composites

AbstractHalloysite nanotubes (HNT) and montmorillonite (Mt) were modified by a novel, dicarboxylic fatty acid substituted amido‐imidazolium chloride. It was found that the modification process of the clays by the imidazolium compound improved their dispersion in the polymer matrix, while HNT were a more beneficial filler of PP than Mt. PP/imidazolium modified HNT composites (PP/HNT‐M) showed significant increase in thermo‐oxidative stability, flexibility, and toughness, combined with a slight reduction in stiffness, as well as a lack of changes in crystallinity and strength, compared with neat PP. These effects were not observed for PP/Mt composites. The formation of strong interactions between the imidazolium compound and tubes' surfaces was supposed to be responsible for the more advantageous properties of PP/HNT‐M composites.

Machine Learning and Structural Design to Optimize the Flame Retardancy of Polymer Nanocomposites with Graphene Oxide Hydrogen Bonded Zinc Hydroxystannate.

Designing flame-retardant polymers with high performance is a long-standing challenge, partly because of the time-consuming traditional approaches based on experiential intuition and trial-and-error screenings. Inspired by the effective new paradigm of data-driven material discovery, we used machine learning to analyze experimental data to accelerate the development of new flame-retardant polymers. To explore the relationship between limit oxygen index (LOI) and components, we prepared 20 composites and then trained a simple equation for the LOI using the method sure independence screening and sparsifying operator (SISSO). The data analysis allows us for a better understanding of the flame-retardant mechanism and components, and the equation has good accuracy in guiding the design of composites with high flame-retardant performance. Meanwhile, the increasing structural design of flame retardants is crucial to flame-retardant polymer composites. We proposed a structure of nano graphene oxide (GO) wrapped micro zinc hydroxystannate (ZHS) in a simple but effective way as a novel flame-retardant agent to enhance the flame retardancy and mechanical properties of polypropylene (PP) composites. The GO sheets were like "light yarns" wrapped onto the ZHS via hydrogen bonding in an ethanol solution. The selected samples were analyzed to confirm the predictive LOI model. The resultant composites with the substitution of intumescent flame retardant (IFR) by 1.0, 2.0, and 4.0 wt % ZHS@GO conferred better flame retardancy compared with PP composite containing only IFR, reflected by the efficient increase of LOI value and V0 rating of UL-94 vertical tests. The analysis principles and facile fabrication strategies proposed in this work could be important for developing highly flame retardant composites.

Effects of Chromic Treatment on the Surface Properties of Polypropylene (PP) Wood Composites

The moisture sensitivity of wood–polymer composites (WPCs) is mainly related to their hydrophilic wood components. Coatings are among the alternatives that improve the dimensional stability of these composites. However, the adhesion of most coatings to the WPC surface is generally poor. Thus, chemical and/or mechanical treatments should be applied to the WPC surface to improve the coating adhesion. Therefore, the main objective of this study was to improve the adhesion coating of polypropylene (PP) WPCs through a chromic treatment. PP was reinforced by three different pulp fibers (kraft, thermomechanical (TMP), and chemothermomechanical (CTMP)) at three fiber contents (50, 60, and 70% w/w). A chromic treatment was applied to the PP-based WPCs to activate the surface of the composites and alter their roughness parameters, creating a higher interfacial zone that improved the bonding of the epoxy coating to the surface of the PP composites. The chromic treatment increased the roughness of the surface. An increase in profile and surface parameters was observed after treatment. This treatment modified the chemical composition of the surface by creating polar carbon–oxygen groups and increasing the carbonyl and hydroxyl indexes.

Influences of 4ZnO·B2O3·H2O whisker based intumescent flame retardant on the mechanical, flame retardant and smoke suppression properties of polypropylene composites

AbstractIn this work, the influences of 4ZnO·B2O3·H2O zinc borate (ZB) whisker based intumescent flame retardant (IFR) containing ammonium polyphosphate and dipentaerythritol on the mechanical, flame retardant and smoke suppression properties of polypropylene (PP) composites were characterized by the universal testing machine, UL‐94, limiting oxygen index (LOI), and cone calorimeter tests, respectively. The results indicate that only 1 phr of ZB could effectively improve the LOI value and slow down the burning rate of PP composite. The peak heat release rate, average of HRR, total heat release, peak smoke production rate, and total smoke production values are all decreased from 413.8 kW/m2, 166.3 kW/m2, 82.3 MJ/m2, 0.0995 m2/s, and 17.9 m2 for PPc/20IFR composite to 267.8 kW/m2, 128.3 kW/m2, 66.8 MJ/m2, 0.0478 m2/s, and 12.6 m2 for PPc/20IFR/1ZB composite, respectively. The scanning electron microscopy images, energy dispersive spectrometry, and Raman spectra of char residue reveal that ZB is helpful to form a compact and graphitized intumescent char residue so that the heat diffusion and oxygen transmission are greatly hindered. The thermogravimetry analysis‐fourier transform infrared spectroscopy (TGA‐FTIR) results show that less combustible volatiles and more H2O vapor are generated with the appearance of ZB. Hence, the combustion mechanism in gas phase is suppressed.

Effect of Alkaline Treatment and Coupling Agent on Thermal and Mechanical Properties of Macadamia Nutshell Residues Based PP Composites

The influence of alkaline treatment on the thermal and mechanical properties of polypropylene (PP) reinforced with fibers from macadamia nutshell (5 to 30 wt%) was studied. To improve the interaction between fiber and matrix, the fibers were submitted to an alkaline treatment, as well as a coupling agent (MAPP) was used. The composites were obtained in a thermokinetic mixer, milled, and injected. Then, the degradation temperature and the loss of mass of the composites, pure PP, and fibers were evaluated. The mechanical properties of the composites were also evaluated. The results indicated that the degradation peak of composites occurred at higher temperatures, which indicated that composite exhibited higher thermal stability at higher temperatures. The addition of raw and treated macadamia fibers to the PP increased the stiffness of the composites, as well as the use of a coupling agent when compared to the neat PP. However, the incorporation of 30 wt% treated fiber to the PP showed an enhancement of 67.5% in the tensile modulus. The morphological analysis enabled to evaluate the efficiency of the coupling agent and the treated fibers adhered to matrix. The response surface methodology (RSM) technique showed that the higher fiber content added to the PP enhanced the stiffness, and consequently reduced the impact strength of the materials.

Effects of difference in shape of carbon black particles on mechanical properties of polypropylene composites with hybridized silica nanofillers with carbon black particles

Effects of difference in shape of carbon black particles on mechanical properties of polypropylene composites with hybridized silica nanofillers with carbon black particles

Investigation on the effect of fiber reinforcement style on shear properties of polypropylene composites

Investigation on the effect of fiber reinforcement style on shear properties of polypropylene composites

Synergistic effect of fly ash on hydroxymethylated lignin‐containing flame retardant polypropylene: Flame retardancy and thermal stability

In this study, fly ash (FA) was used as a synergist to enhance the fire resistance of intumescent flame retardant polypropylene containing hydroxymethylated lignin. Effects of fly ash on flame retardancy and thermal stability properties of polypropylene (PP) composites were investigated using a limiting oxygen index (LOI) meter, UL‐94 vertical combustion tester, cone calorimeter, and thermogravimetric analyzer. The results showed that during combustion, incorporation of FA can effectively solve the dripping problem of the PP composites. Addition of 0.5% loading amount fly ash into the PP composite (0.5FA/IFR/PP) enhanced the flame retardancy significantly. Additionally, its LOI value increased from 28% to 33%, and UL‐94 vertical burning passed V‐0 grade from V‐2 rate. Notably, owing to addition of the fly ash, the peak of heat release rate of the pure PP decreased by 58.0%. Moreover, the release of CO2 and CO was largely suppressed, and higher char residue was obtained for 0.5FA/IFR/PP. Fire safety of the PP composites was significantly improved. From the analysis of charring residues, a possible flame retardant mechanism was proposed. That is, incorporation of fly ash increased the formation of a denser and intact char layer, which is important in inhibiting heat and flammable gases generated during combustion of underlined matrix.