Reinforced Polypropylene Composites Research Articles

Thermal Effects on Tribological Behavior in Machining Natural Fiber Composites

Machining natural fibers reinforced plastic (NFRP) composites is nowadays a real challenge for academia and industries. These eco-friendly materials are emerging in automotive and aeronautical industries thanks to many benefits for sustainable development. It is then necessary to anticipate their machining processes for integrating them into the NFRP industrial production chains. This paper investigates the thermal effect on the machinability of unidirectional flax fibers reinforced polypropylene composites (UDF/PP) regarding to the cutting contact geometry. For this aim, orthogonal cutting process has been performed on UDF/PP composites at room and low temperature of composite samples. Cutting contact geometry has been explored by changing the tool rake angle. Results show that reducing the cutting temperature affects the chip morphology and improves the cutting behavior of flax fibers which ameliorates the machinability of UDF/PP composites. This machinability is also improved by cutting with a smaller positive rake angle that increases the cutting contact stiffness with flax fibers. This study allows determining a new relevant indicator parameter of NFRP machinability based on the cutting friction.

Effect of Weave Structure and Yarn Density on Mechanical Attributes of Jute Fabric Reinforced Polypropylene Composites

This paper represents a comparative study of the different weave structures of jute woven fabric reinforced polypropylene (PP) composites. The weave structures were selected as plain (1/1), twill (2/1), twill (3/1) and basket (2/2). Composites (40% fiber by wt.) were prepared by using compression molding technique. The mechanical properties such as tensile strength (TS), bending strength (BS) and impact strength (IS) of the composites were evaluated and compared. It was found that basket weave/PP based composite showed the highest mechanical properties. The optimum value of TS, BS, TM, BM and IS of the composite were found to be 49.7 MPa, 92.5 MPa, 867 MPa, 5.6 GPa and 29.8 KJ/m2.To find out the effect of yarn density on mechanical properties of the composites, 2/1 twill structure was selected and found significant improvement in the mechanical properties with the increase of Ends/Inch (EPI) and Picks/Inch (PPI) in the fabric. Water uptake and degradation behavior in aqueous medium of the composites was also observed.

Thermo-mechanical Effects in Mechanical Polishing of Natural Fiber Composites

Efficient machining and finishing of natural fiber reinforced plastic (NFRP) composites is essential for realizing the industrial application envisaged of these promising, environmentally friendly materials. While prior efforts allude to the multiscale nature of their material removal mechanisms, little understanding currently exists on the thermal effects of their material removal behaviors. This experimental study aims to characterize the thermal effects during the polishing of NFRP composites. For this aim, dry and wet polishing have been performed following several polishing steps on unidirectional flax fibers reinforced polypropylene composites. Results from scanning electron microscopy (SEM) and optical interferometry studies reveal a significant difference between dry and wet polishing in terms of surface artifacts induced. This difference is enhanced at higher sliding speed, indicating that the asperity removal during polishing is mostly thermally mediated. The results also indicate that the surface forming of flax fibers is related to the mechanical contact scale engendered by the grit size.

Study on strain-rate-dependent behaviour and constitutive model of long glass fibre reinforced polypropylene composite

Accurate material model under different strain rates (˙e) is important for numerical simulations in vehicle design and crashworthiness assessment. Therefore, the objectives of this study are to develop the constitutive model of long glass fibre reinforced polypropylene composite (hereinafter referred to as 'LGFRP') which related to strain rate range of 10-3/s-50/s. Tensile and compression tests are conducted at different strain rates. The experimental results show that the failure strain and ultimate strength increase as increasing strain rate. The elastic modulus is sensitive to strain rate in tensile tests, but less sensitive to strain rate in compression tests. According to the experimental results, a novel constitutive model proposed by the authors is used to represent stress-strain relationship related to strain rate of the LGFRP. The analysis results show that the novel constitutive model agrees well with the experimental results.

Tribological and mechanical performance of sisal-filled waste carbon and glass fibre hybrid composites

Abstract This study has been carried out to show the use of natural fibres as the potential substitute of synthetic fibres in tribo-composites. The abrasive wear behaviour and mechanical properties of waste sisal/glass, sisal/carbon hybrid fibre reinforced polypropylene (PP) composites were analysed in this study. Results showed that increasing the sisal fibre weight content in the composites increases the coefficient of friction. The abrasion volume of sisal/glass hybrid composites showed significantly lower than those of sisal/carbon hybrid composite for the same hybrid ratios. This means that addition of sisal fibres on waste carbon and glass fibre reinforced PP composites decreased the potential of tribological performance. Although adding of sisal fibres as a natural substitute fibre source to waste short carbon fibre composites lead to inferior properties, an addition of sisal fibres to waste glass composites shows lower densities, comparable mechanical and abrasion volumes than that of waste glass fibre composites. This shows that sisal fibres can be used in place of glass fibres. The scanning electron micrographs of the fracture surfaces show that the wetting interaction of sisal and glass fibre with PP matrix is better than those of the sisal carbon hybrid composites. Furthermore, the worn surfaces of the sisal and its hybrid composites show vertical cracks, loose fragments, micro ploughing and transfer layers.

Towards selection chart of flame retardants for natural fibre reinforced polypropylene composites

Abstract The market of natural fibre thermoplastic composites NFTC is still developing. However, it is limited by the progress in optimising the process parameters and defining the functional additives. One of the most needed additives is the flame retardant FR material. Addition of excessive FRs can decrease the mechanical properties. Polypropylene PP reinforced with 30% natural fibres (flax, jute, hemp and sisal) are prepared using kneading and different FRs are mixed together. The effect of the different FRs on the flame retardance level, namely UL94, as well as the mechanical properties are studied. The studied FRs materials in this work are mineral, halogenated, halogen-free intumescent. Also, the effect of synergism with nanoclays and antimony trioxide is considered. Based on the mechanical properties and the flame retardance levels, a concept of FR selection chart is built considering only the both aspects of the tensile strength and flame retardance test UL94.

Coir Fiber Reinforced Polypropylene Composites: Eco-friendly Byproducts

Coir fiber (CF) reinforced polypropylene (PP) composites were fabricated using an extruder machine. The fiber contents were varied 5 to 20% and physico-mechanical properties as well as bio-degradability were also tested. Ultimate tensile strength and flexural strength decreases with the increases of percentages of fiber addition. Lowest percentage elongation is observed at 20% CF+PP composite which are rigid in nature. Leeb rebound hardness also decreases with the increase of percentage of raw fiber addition. The bio-degradation of different percentage of CF and PP composites in soil and saline water increased with increase of coir fiber content. Thus, it showed that higher percentage of coir fiber was produced more biodegradable and eco-friendly byproducts. However, higher percentages of coir fiber decrease the mechanical properties. A moderate percentage of coir fiber i.e. 15% CF +PP showed the good mechanical properties as well as considerable amount of bio-degradability in soil and saline water.J. Environ. Sci. & Natural Resources, 10(1): 61-64 2017

Glass fiber–reinforced polypropylene composites fabricated by direct fiber feeding injection molding

Abstract This article investigates the effect of process parameters on the mechanical properties of polypropylene-glass fiber (GF/PP) composites made using a new injection molding method known as direct fiber feeding injection molding (DFFIM). In the DFFIM process, continuous fibers are directly guided into the barrel of the injection molding machine through the designed vent and are fed into the polymer melt by the shearing motion of the screw of the injection molding machine during the plasticization process. The DFFIM process improves the fiber length and avoids excessive fiber attrition, resulting in enhanced mechanical properties in the composites. The effect of process parameters on the mechanical properties of manufactured composite specimens is discussed based on the results of tensile tests, three-point flexural tests, and Izod impact tests. Scanning electron microscopy was performed on the fracture surfaces to observe cross-section morphology. There is a fiber agglomeration phenomenon that occurs in the core layer of GF/PP composites made using DFFIM. The number of fiber rovings, number of fiber filaments, matrix feeding speed, and screw speed influence the GF content and distribution in the composites, ultimately affecting the mechanical properties.

Characteristics on Treated Kenaf Fiber Reinforced Polypropylene Composites

Nowadays natural fiber and polymer matrix are being extensively used as alternatives in producing furniture like ceiling, floor and etc. to fulfill society demand instead of environmental friendly and saving cost. The objective of this study is to investigate the effects of maleic anhydride grafted polypropylene (MAPP) as a coupling agent for reinforcement between kenaf fiber (KF) and polypropylene (PP). The ratio of MAPP between 3% and 5% was observed to determine which composition ratio is better. The tensile strength for both 30% KF and 40% KF was treated through the alkali treatment process with 5% sodium hydroxide (NaOH). Kenaf fiber reinforced polypropylene (PP/KF) composites were melt blended and then used hydraulic molding test press machine for characterization to observe their tensile strengths by measuring their threshold. Tensile test was carried out to determine the tensile stresses of the composite at the best composition ratio of kenaf fiber that are 30% KF and 40% KF instead of MAPP ratio. The result shows 40% KF (5% MAPP) lead to better tensile performance compared to 40% KF (3% MAPP), 30% KF (5% MAPP) and 30% KF (3% MAPP). Meanwhile, Scanning electron microscopy (SEM) is used to observe the morphological comparison between untreated KF and treated KF as well as PP/KF. The good interfacial bonding between KF and PP was 5% MAPP rather than 3% MAPP due to the optimum strength received. Overall 5% MAPP with 40% PP/KF had shown the best result compared to others with the estimated tensile strength value of 21.38 MPa.

Characterization of dimensional stability in flax fiber reinforced polypropylene composites

Flax fibers are a sustainable and high performance reinforcement for polymer composites. Molding polymers and polymer composites nearly always results in warpage or compromised “dimensional stability” of the part. However, there are very few reports on the quantitative analysis of dimensional stability, especially for natural fiber reinforced polymer composites. A systematic study of the dimensional stability of flax fiber reinforced polypropylene (PP) composites is undertaken by measuring the shrinkage of the composites after molding. Shrinkage is directly related to dimensional stability. Using flax fibers decreases part shrinkage or increases dimensional stability. Shrinkage in the molding flow direction is less than shrinkage perpendicular to it, which is shown to be a result of fiber orientation in that direction. Using maleic anhydride modified PP as a coupling agent further decreases the shrinkage. It is found that less shrinkage occurs in composites of higher modulus. POLYM. COMPOS., 40:132–140, 2019. © 2017 Society of Plastics Engineers

Characterization of nonlinear response in quasi-unidirectional E-glass fabric reinforced polypropylene composites under off-axis tensile loading

The present paper addressed the nonlinear stress-strain response in quasi-unidirectional E-glass fabric reinforced polypropylene composites under off-axis tensile loading. A series of monotonic and cyclic loading-unloading tensile tests were carried out. Both irreversible strains and stiffness degradation were observed in cyclic loading-unloading tests, which indicate that the nonlinear response of composites was induced by a combination of damage and plasticity. A coupled damage-plasticity model was employed to describe the nonlinear off-axis tensile stress-strain relation of materials. In this model, a plastic potential function together with associated plastic flow rule were adopted to assess the evolution of plastic strains. The damage variables in forms of stiffness degradation were expressed as a Weibull function of the effective stress. A full suite of model parameters was experimentally determined from cyclic loading-unloading tensile tests. The stress-strain curves predicted by this model agreed well with experimental results.

Foam injection molding of glass fiber reinforced polypropylene composites with laminate skins

Sandwich panels which consist of discontinuous glass‐fiber reinforced polypropylene composite foam core and continuous glass‐fiber reinforced polypropylene laminate skins were manufactured using industry‐scale equipment in a streamlined manner. The streamlined process included two stages: (1) continuous glass‐fiber reinforced polypropylene laminates as the face skins were produced using an automated, rapid tape layup machine and a hydraulic press, and (2) discontinuous glass‐fiber reinforced polypropylene composite as the core was foam injection‐molded onto the laminate skins (i.e., overmolding), which eliminated bonding process of the foam core and laminate skins, with a physical blowing agent, nitrogen. Optical microscopy results suggested that the increase of void fraction by the core‐back (or mold opening) technique increased the average cell size and cell size distribution, but had little effect on the cell density of the foam core. Mechanical test results suggested that the addition of laminate skins increased the flexural modulus and flexural strength of the solid as well as foam composites significantly. In addition, the material indices were calculated for the sandwich panels manufactured in this study, and the results suggested that the addition of the laminate skins and foaming by the core‐back (or mold opening) technique can greatly reduce the weight of material needed to have the same bending stiffness and maximum bending force. COMPOS., 39:4322–4332, 2018. © 2017 Society of Plastics Engineers

Characterizing the Mechanical Properties of Fused Deposition Modelling Natural Fiber Recycled Polypropylene Composites

The objective of this investigation was to characterize the performance of natural fiber reinforced polypropylene composites in fused deposition modelling (FDM). Composite filaments comprising of pre-consumer recycled polypropylene with varying contents of hemp or harakeke fibers were extruded from which tensile test specimens were made using FDM. Filament and test specimens were tensile tested and properties were compared with plain polypropylene samples; the ultimate tensile strength and Young’s modulus of reinforced filament increased by more than 50% and 143%, respectively, for both 30 wt % hemp or harakeke compared to polypropylene filament. However, the same degree of improvement was not seen with the FDM test specimens, with several compositions having properties lower than for unfilled polypropylene. SEM analysis of fracture surfaces revealed uniform fiber dispersion and reasonable fiber alignment, but porosity and fiber pull-out were also observed. Fiber reinforcement was found to give benefit regarding dimensional stability during extrusion and FDM, which is of major importance for its implementation in FDM. Recommendations for optimization of processing in order to enhance build quality and improve mechanical properties are provided.

Behavior of the interphase of dyed cotton residue flocks reinforced polypropylene composites

Abstract Textile industry produces a high amount of residues that, nowadays, are poorly managed. The majority of such wastes are dumped and landfilled. Among all the textile value chain, cotton yarning factories produce wastes in the shape of fiber flocks, with lengths smaller than 10 mm that prevent their reintroduction in the textiles manufacturing process. Nonetheless, such waste cotton flocks could be used as reinforcement for short fiber mould injected composites. This paper reports on the behavior of the interphase between the cotton flocks and a polypropylene matrix. It was found that the organic dyes present on the cotton flocks seem to affect the quality of the interphase in two ways: on the one hand by increasing the affinity between the cotton fibers and the matrix, and on the other hand by limiting the effect of the coupling agents. Micromechanic models are used to further research the quality of the interphase and the intrinsic properties of the composites.

Effect of gamma irradiation aging on mechanical and thermal properties of alfa fiber–reinforced polypropylene composites

Recently, the interest in plant fiber composites has considerably increased due to the new environmental legislation as well as consumer pressure that forced manufacturing industries to search substitutes to the conventional materials. The aim of this article is to assess the effects of different does of gamma irradiation on the physico-mechanical properties of the composites PP / alfa fiber treated and untreated. The Young’s modulus of composites increases in the presence of alfa fiber and it was more pronounced with untreated ones resulting by the cross-linking, whereas elongation and maximum strain decreased as dose irradiation raised. Fourier transform infrared spectroscopy results showed that the virgin PP has better stability to gamma irradiation than treated and untreated composites. Thermogravimetric analysis showed that the addition of the treated and untreated fiber greatly improves the thermal stability of the polymer matrix before and after gamma irradiation. Composites based on treated and untreated fiber have better storage modulus than virgin matrix.

Short Jute Fiber Reinforced Polypropylene Composites: Effect of Nonhalogenated Fire Retardants

Short jute fiber reinforced polypropylene (PP) composites were prepared using a single screw extrusion moulding. Jute fiber content in the composites is optimized with the extent of mechanical properties, and composites with 20% jute show higher mechanical properties. Dissimilar concentrations of several fire retardants (FRs), such as magnesium oxide (MO), aluminum oxide (AO), and phosphoric acid (PA), were used in the composites. The addition of MO, AO, and PA improved the fire retardancy properties (ignition time, flame height, and total firing time) of the composites. Ignition time for 30% MO, flame height for 30% PA, and total firing time for 20% MO content composites showed good results which were 8 sec, 1 inch, and 268 sec, respectively. Mechanical properties (tensile strength, tensile modulus, bending strength, bending modulus, and elongation at break), degradation properties (soil test, weathering test, and percentage of weight loss), and water uptake were studied.

Micro-milling of unreinforced and reinforced polypropylene

It is essential to determine the micro-machinability performance of polymer and glass fiber–reinforced polymer composite in order to effectively utilize the polymer and its composite as an engineering material at the micro-scale world. However, a literature survey revealed that not much work was done on the micro-milling of polymer and its composite. In the light of literature surveys, it can be said that the novelty of this study is to investigate the micro-milling performance of polypropylene and glass fiber–reinforced polypropylene manufactured with plastic injection molding process. The tests were performed at different feed rates and spindle speeds and the effect of these parameters on tool wear, burr width and micro-milling forces was investigated. In general, it was concluded that wear and forces in micro-milling of reinforced polypropylene composite were higher than that of unreinforced polypropylene. Micro-milling forces increased with feed rate and spindle speed for both materials. The lowest top burr size and force values were obtained at the feed of 50 mm/min and the spindle speed of 20,000 r/min. Unreinforced polypropylene gave better performance with respect to glass fiber–reinforced polypropylene composite from micro-machinability aspect.

Manufacturing of recycled carbon fiber reinforced polypropylene composites by high speed thermo‐kinetic mixing for lightweight applications

Recycled carbon fiber reinforced polypropylene (PP) composites were fabricated by using high speed thermo‐kinetic mixer. The effect of recycled carbon fiber on the morphological, chemical, physical, thermal, and mechanical properties of PP composites was investigated. The results indicate that the tensile and flexural strength of PP increase with addition of recycled carbon fiber up to 20 wt%. When 40 wt% recycled carbon fiber was added into PP, the tensile and flexural moduli were increased by about 177 and 359%, respectively. The coefficient of thermal expansion was found to be decreased by increasing recycled carbon fiber weight fraction. The addition of low weight fraction of recycled carbon fibers (up to 5 wt%) increased the nucleation process on PP crystallization. POLYM. COMPOS., 39:3656–3665, 2018. © 2017 Society of Plastics Engineers

Microdebond test development and interfacial shear strength evaluation of basalt and glass fibre reinforced polypropylene composites

Interfacial adhesion of basalt and glass fibre reinforced polypropylene composites was studied using microdebond testing technique. A focus was put on a simple approach of applying extruded thermoplastic films as a matrix material for microdroplet formation. The ability of different viscosity and thickness polypropylene films to form symmetrical droplets under a temperature range of 200–240℃ was evaluated. Emphasis was put on polypropylene matrix chemistry, silane fibre surface treatment and testing loading rate impact on interfacial performance change in polypropylene-basalt fibre and polypropylene-glass fibre microcomposites. It was found that it was possible to obtain high symmetrical droplet yield out of polypropylene films of melt flow rate 50 and 125 g/10 min and 55–85 µm thickness at 240℃. The presence of maleic anhydride grafted polypropylene coupling agent increased the interfacial shear strength significantly. Microcomposites with glass fibre had higher interfacial shear strength in comparison with the used basalt fibre, mainly due to the difference in their sizing. Various silane-based fibre surface coatings did not result in significant interfacial adhesion changes. Polypropylene-glass fibre microcomposite interfacial shear strength at 0.5, 3.0 and 10.0 mm min–1 loading rates had similar values with high maximum pull-out force scatter at 0.5 and 3.0 mm min–1 loading rates and low scatter at 10.0 mm min–1.

The Influence of Alkaline Treatment of Plant Fibres on Tensile Properties of Single Fibres and Composites

The hypothesis pursued in this work is that by removing hemicellulose and pectin from plant fibres by alkaline treatment, the fibre tensile performance could be improved. Flax fibres were examined as reinforcement. The highest ultimate tensile strength (UTS) resulted for fibre treated with 3% by weight of NaOH solution (up to 12% increase in UTS and 18% increase in Young’s modulus, compared to untreated fibres). A 15% reduction in cross-sectional area of the fibres was observed. Tensile performance of treated (a percentage of fibre volume fraction (Vf %) of 30%) and untreated (Vf % of 34%) fibre reinforced polypropylene composites manufactured by the vacuum forming process, were compared. A decrease of UTS and Young’s modulus of the treated material was observed with an increase in consolidation time. The UTS of the treated material was 3.82% lower than that of the untreated material.