Flexural and impact response of woven glass fiber fabric/polypropylene composites

Impact tests with a falling dart and flexural measurements were carried out on polypropylene based laminates reinforced with glass fibers fabrics. Research has shown that the strong fiber/matrix interface obtained through the use of a compatibilizer increased the mechanical performance of such composite systems. The improved adhesion between fibers and matrix weakly affects the flexural modulus but strongly influences the ultimate properties of the investigated woven fabric composites. In fact, bending tests have shown a clear improvement in the flexural strength for the compatibilized systems, in particular when a high viscosity/high crystallinity polypropylene was used. On the contrary, the low velocity impact tests indicated an opposite dependence on the interface strength, and higher energy absorption in not compatibilized composites was detected. This result has been explained in terms of failure mechanisms at the fiber/matrix interface, which are able to dissipate large amounts of energy through friction phenomena. Pull-out of fibers from the polypropylene matrices have been evidenced by the morphological analysis of fracture surfaces after failure and takes place before the fibers breakage, as confirmed by the evaluation of the ductility index.     

Tailoring of dual-interface in high tenacity PP composites – Toughening with positive hybrid effect

The study proves the feasibility of manufacturing injection moulded polypropylene composites reinforced with short rayon cellulose fibres of two selectively tailored fibre–matrix interfaces. The originally developed method relies on selective chemical grafting of two different polymer waxes onto the surface of cellulose fibres in order to obtain two different strengths of fibre–matrix interfaces in one composite. This selective tailoring of a dual-interface is meant to improve the notched impact strength without deteriorating of its flexural strength. Compatibilised fibres have a strong interphase, which conditions the transfer of strain from the matrix to fibres during deformation. Fibres tailored for a weak interface more efficiently hinder the crack propagation at crash. A 32% improvement of composite notched impact strength was achieved with merely a 5% deterioration of its flexural strength. Its specific properties are on the level or better than those of polypropylene counterpart reinforced with the same content of glass fibres.     

Reinforcement of polypropylene with hemp fibres

Noil hemp fibre (NHF) is a kind of textile hemp fibre after deep degumming from scutched hemp fibre (SHF), mechanically-degummed hemp fibre. Both NHF and SHF with strong mechanical properties are good candidates as reinforcing fibres for plastics such as polypropylene (PP). The PP/NHF and PP/SHF composites were blended via internal mixing process. The effect of fibres on the morphology, thermal resistance and reinforcement of the composites were investigated. PP/NHF composites showed higher impact strength, lower flexural strength than PP/SHF at the corresponding loading because NHF has smaller diameter and better thermal resistance than SHF. Meanwhile, NHF has the similar reinforcement to tensile strength with SHF. The effect of maleic anhydride polypropylene (MAPP) on the fibre-resin interface bonding was also comparatively studied. With increasing amount of MAPP, the tensile, flexural and impact strengths of PP/NHF and PP/SHF increased, respectively. The morphology of PP/SHF and PP/NHF results well showed that MAPP improved the interaction of the fibres with PP through chemical adhesion.     

Experimental and theoretical studies on the properties of injection moulded glass fibre reinforced mixed plastics composites

Recycled mixed post-consumer and post-industrial plastic wastes consisting of HDPE, LDPE and PP were injection moulded with short glass fibre (10–30% by weight) to produce a new generation composite materials. Intensive experimental studies were then performed to characterise the tensile, compression and flexural properties of glass fibre reinforced mixed plastics composites. With the addition of 30 wt.% of glass fibre, the strength properties and elastic modulus increased by as much as 141% and 357%, respectively. The best improvement is seen in the flexural properties due to the better orientation of the glass fibres in the longitudinal direction at the outer layers. The randomness and length of the glass fibre were accounted to modify the existing rule of mixture and fibre model analysis to reliably predict the elastic and strength properties of glass fibre reinforced mixed plastics composites.     

Polyolefin composites with curaua fibres: Effect of the processing conditions on mechanical properties,morphology and fibres dimensions

Composites of polypropylene (PP) and high density polyethylene (HDPE) reinforced with 20 wt.% of curaua fibres were prepared using a twin-screw extruder and the effect of screw rotation speed (SRS) was evaluated by measuring the output, the mechanical properties of the composites, the morphology and the fibre dimensions. Increase in SRS causes a decrease in length, diameter and aspect ratio of the fibres in both composites, due to the high shear forces acting in the molten polymer and transferred to the fibres. Consequently, the reinforcement effect of the fibres decreased, as evidenced by the flexural and tensile mechanical properties of the composites. Additionally, polymeric matrices undergoes thermo-mechanical degradation during processing, this also contributed to the changes in the mechanical properties. Comparison between the matrices showed that PP composites are less affected by changes in SRS, suffering fewer changes in fibre dimensional parameters and in the mechanical properties than HDPE composites.     

Biocomposites from Musa textilis and polypropylene: Evaluation of flexural properties and impact strength

Abaca (Musa textilis)-reinforced polypropylene composites have been prepared and their flexural mechanical properties studied. Due to their characteristic properties, M. textilis has a great economic importance and its fibers are used for specialty papers. Due to its high price and despite possessing very distinctive mechanical properties, to date abaca fibers had not been tested in fiber-reinforced composites. Analysis of materials prepared showed that, in spite of reduced interface adhesion, flexural properties of the PP composites increased linearly with fiber content up to 50 wt.%. Addition of a maleated polypropylene coupling agent still enhanced the stress transfer from the matrix to the reinforcement fiber. As a result, composites with improved flexural properties were obtained. The mechanical properties of matrix and reinforcing fiber were evaluated and used for modelling both the flexural strength and modulus of its composites. In addition, the impact strength of materials was evaluated. Comparison with mechanical properties of composites reinforced with fiberglass points out the potentiality of abaca-reinforced polypropylene composites as suitable substitutes in applications with low impact strength demands.     

Polypropylene/glass fibre 3D-textile reinforced composites for automotive applications

Textile-reinforced thermoplastic composites offer huge application potentials for a rapid manufacturing of components with versatile possibilities of integrating functions. However, an application of these new materials requires the knowledge of the directional dependent material properties. In this study, results are presented concerning selected relevant load cases for industrial applications. For the new group of multi-layered flat bed weft-knitted glass fibre/polypropylene composites (MKF-GF/PP), tensile tests under different temperatures and test velocities have been carried out as well as Charpy impact tests, open hole tension tests and dynamic-mechanical analysis. The mechanical properties of MKF-GF/PP and unidirectional GF/PP composites with tailored fibre surface and interphase, respectively, have been compared to those of woven GF/PP composites and GF/PP composites made of non-crimp fabrics (NCF) as a benchmark.     

Effect of glass fiber hybridization on properties of sisal fiber–polypropylene composites

Natural fiber reinforced polymer composites became more attractive due to their light weight, high specific strength, and environmental concern. However, some limitations such as low modulus, poor moisture resistance were reported. This study aimed to investigate the effect of glass fiber hybridization on the physical properties of sisal–polypropylene composites. Polypropylene grafted with maleic anhydride (PP-g-MA) was used as a compatibilizer to enhance the compatibility between the fibers and polypropylene. Incorporating glass fiber into the sisal–polypropylene composites enhanced tensile, flexural, and impact strength without having significant effect on tensile and flexural moduli. In addition, adding glass fiber improved thermal properties and water resistance of the composites.     

The use of a mixed coupling agent system to improve the performance of polypropylene-based composites reinforced with short-glass-fibre mat

In order to improve the mechanical properties of composites consisting of polypropylene reinforced with mats of short glass fibres, the fibre surface was treated with a silane coupling agent, N-β(N-vinylbenzylaminoethyl)-γ-aminopropyl trimethoxy silane hydrogen chloride (STS), and a titanate coupling agent, isopropyltriisostearoyl titanate (TTS). The flexural properties and the impact absorption energy of these composites were measured as a function of coupling agent concentration. STS-only treatment of the fibre surface enhanced the flexural strength and the flexural modulus of the composite, while TTS-only treatment decreased the flexural strength and the flexural modulus. The improved flexural properties of the composite brought about by the STS-only treatment were obtained at the cost of its impact absorption energy, whereas TTS-only treatment showed the inverse characteristics. However, in a mixed coupling agent system, the impact absorption energy of the composite was improved without a reduction in the flexural properties. A morphological study of the fracture surfaces of the composite after impact testing, void content measurement and single-fibre fragmentation test were also carried out to understand the interfacial phenomena of the surface treated composites.     

Effect of coupling agents on reinforcing potential of recycled carbon fibre for polypropylene composite

Polypropylene (PP) composites reinforced with recycled carbon fibre have been prepared through extrusion compounding and injection moulding. The reinforcing potential of the recycled fibre was increased by improving the interfacial adhesion between the fibre and PP matrix and this was done by the addition of maleic anhydride grafted polypropylene (MAPP) coupling agents. Three MAPP couplers with different molecular weights and maleic anhydride contents were considered. The effects on the mechanical properties of the composite were studied, and scanning electron microscopy (SEM) was used to study the fracture morphology of the tensile specimens. It was observed that with the addition of MAPP the interfacial adhesion was improved as fewer fibres were pulled-out and less debonding was seen. A microbond test was performed and a significant improvement in interfacial shear strength was measured. This resulted in composites with higher tensile and flexural strengths. The maximum strength was achieved from MAPP with the highest molecular weight. Increased modulus was also achieved with certain grades of MAPP. It was also found that the composite impact strength was improved significantly by MAPP, due to a higher compatibility between the fibre and matrix, which reduced crack initiation and propagation.     

Continuous-glass-fibre-reinforced polypropylene composites: I. Influence of maleic-anhydride-modified polypropylene on mechanical properties

This study investigates the influence of maleicanhydride-modified polypropylene (m-PP) on monotonic mechanical properties of continuous-glass-fibre-reinforced polypropylene (PP) composites. Maleicanhydride-modified polypropylene was added to the PP homopolymer to improve the adhesion between the matrix and the glass fibre. Three-point bending tests were performed on 0° and 90° unidirectional glass-fibre/PP laminates with various weight fractions of m-PP in the PP matrix. These tests showed an increase in both longitudinal and transverse flexural strength up to 10 wt% m-PP, whereas at higher weight fractions of m-PP a decrease in flexural strength was observed. No significant influence of m-PP on composite stiffness was observed. Additional mechanical tests on unidirectional glass/PP composites with 0 wt% and 10 wt% m-PP showed only a small increase in fibre-dominated properties such as longitudinal tensile strength and strain, whereas composite properties that are governed by the interphase, such as transverse, shear and compressive strength, showed significant increases as a result of matrix modification and an enhanced interaction between the glass fibres and the PP matrix.     

Polypropylene composites with enzyme modified abaca fibre

Abaca fibre reinforced PP composites were prepared using a high speed mixer followed by injection moulding with 30 wt.% of fibre load. Prior to composite production, the fibres were modified by fungamix and natural enzyme. The effects of modification of the fibre were assessed on the basis of morphology and thermal resistance and as well as on mechanical, thermal and environmental stress corrosion resistance properties of the resulting composites. Coupling agent (MA-PP) was also used with unmodified abaca fibre to observe the coupling agent effect on resulting composites properties. The moisture absorption of the composites was found to be reduced 20–45% due to modification. Tensile strength found to be 5–45% and flexural strengths found to be 10–35% increased due to modification. Modified fibre composites found to better resistance in acid and base medium.     

The effect of reprocessing on the mechanical properties of polypropylene reinforced with wood pulp,flax or glass fibre

Composites of polypropylene, substitutable for a given application and reinforced with: Medium Density Fibreboard fibre (MDF) (40 wt%); flax (30 wt%); and glass fibre (20 wt%), were evaluated after 6 injection moulding and extrusion reprocessing cycles. Of the range of tensile, flexural and impact properties examined, MDF composites showed the best mean property retention after reprocessing (87%) compared to flax (72%) and glass (59%). After 1 reprocessing cycle the glass composite had higher tensile strength (56.2 MPa) compared to the MDF composite (44.4) but after 6 cycles the MDF was stronger (35.0 compared to 29.6 MPa for the glass composite). Property reductions were attributed to reduced fibre length. MDF fibres showed the lowest reduction in fibre length between 1 and 6 cycles (39%), compared to glass (51%) and flax (62%). Flax fibres showed greater increases in damage (cell wall dislocations) with reprocessing than was shown by MDF fibres.     

The effect of fibre content on the mechanical properties of glass fibre mat/polypropylene composites

Glass fibre mat was prepared by the fibre mat-manufacturing machine developed in our laboratory. Glass fibre mat reinforced polypropylene (PP) composites were fabricated with the variation of glass fibre content. Tensile, flexural and high rate impact test was conducted to investigate the effect of glass fibre content on the mechanical properties of the glass fibre mat/PP composite. Deformation and fracture behaviour of the glass fibre mat/PP composites was investigated to study the relationship with the mechanical property data. The tensile and flexural modulus increased with the increment of glass fibre content. However, the tensile and flexural strengths exhibited maximum values and showed a decrease at the higher glass fibre content than this point. The impact absorption energy also exhibited a similar result with the tensile and flexural property data.     

Mechanical and thermal properties of carbon fiber/polypropylene composite filled with nano-clay

The effect of organoclay on the mechanical and thermal properties of woven carbon fiber (CF)/compatibilized polypropylene (PPc) composites is investigated. Polypropylene–organoclay hybrids nanocomposites were prepared using a maleic anhydride-modified PP oligomer (PP-g-MA) as a compatibilizer. Different weight percentages of Nanomer® I-30E nanoclay were dispersed in PP/PP-g-MA (PPc) using a melt mixing method. The PPc/organoclay nanocomposite was then used to manufacture plain woven CF/PPc nanocomposites using molding compression process. CF/PPc/organoclay composites were characterized by different techniques, namely; dynamic mechanical analysis (DMA), fracture toughness and scanning electron microscope. The results revealed that at filler content 3% of organoclay, initiation and propagation interlaminar fracture toughness in mode I were improved significantly by 64% and 67% respectively, which could be explained by SEM at given weight as well; SEM images showed that in front of the tip, fibers pull out during initiation delamination accounting for fracture toughness improvement. Dynamic mechanical analysis showed enhancement in thermomechanical properties. With addition 3 wt.% of organoclay, the glass transition temperature increased by about 6 °C compared to neat CF/PPc composite indicating better heat resistance with addition of organoclay.     

The importance of bonding in intralayer carbon fibre/self-reinforced polypropylene hybrid composites

Polymer composites are usually either stiff or tough, but seldom both. Intralayer hybrids of carbon fibre and self-reinforced polypropylene (PP) do offer the potential to achieve a unique combination of toughness and stiffness. In these hybrids, the bonding between carbon fibre prepregs and PP tapes is a crucial parameter. For a weak bonding, the 20% ultimate tensile failure strain and high penetration impact resistance of self-reinforced PP were maintained. For a strong bonding, the ultimate tensile failure strain was strongly reduced, but the flexural performance was improved. For a homopolymer PP matrix in the prepregs, the weak bonding between fibre and matrix caused the penetration impact resistance to reduce according to a linear rule-of-mixtures. For a maleic anhydride modified PP matrix however, the strong fibre–matrix bonding greatly reduced the penetration impact resistance. These results provide new insights into designing hybrid composites with a unique balance of stiffness and failure strain.     

Early prediction of the failure of textile-reinforced thermoplastic composites using hybrid yarns

In this study, the manufacturing of core-sheath hybrid yarns consisting of steel fibres and glass filament yarn (GFY) using a friction spinning technique and their usability for failure prediction in composites is reported. With the DREF-2000 friction spinning technique, it is possible to manufacture hybrid yarns having a core-sheath structure. Steel fibres are used as the sheath and the GFY is used as the core of the yarns. These hybrid yarns are embedded between two layers of glass/polypropylene (GF/PP)-based knitted fabric composites. By varying the steel fibre content, it is possible to adjust the initial resistance as well as the sensitivity of the hybrid yarns to measure the interphase strain in the thermoplastic-based knit composite during tensile loading. The hybrid yarns with lower steel fibre content are found to be more sensitive in the prediction of the early damage in the composite. By performing a quasi-static and gradual increase of loading during the tensile tests, it is possible to identify the critical load for the composite. The before mentioned hybrid yarns show their suitability for the structural health monitoring and the potential to be integrated into thermoplastic-based composites by textile processing.     

Properties of Wood Fibre-Polypropylene Composites: Effect of Wood Fibre Source

This study examined the effect of type of wood fibre source on the physical and mechanical properties of wood fibre-polypropylene composites. Wood flour, fibres of heat-treated wood and pellets were used as sources of wood fibres in the manufacturing process. All studied wood fibre-polypropylene composites were made from 75% wood, 22% recycled polypropylene (PP) and 3% maleated polypropylene (MAPP). Wood fibre-polypropylene composites were compounded in a conical twin-screw extruder. Water absorption and thickness swelling were studied. Mechanical properties of the composites were characterised by tensile, flexural, and impact testing. Micromechanical deformation processes were investigated using scanning electron microscopy done on the fractured surfaces of broken samples. The durability of composites exposed to three accelerated cycles of water immersion, freezing and thawing was examined. The results showed that the density of the composites was a key factor governing water absorption and thickness swelling. A significant improvement in tensile strength, flexural strength, and Charpy impact strength was observed for composites reinforced with heat-treated fibre compared to composites reinforced with pellets and especially to wood flour reinforced composites. The flexural strength and dimensional stability performance reduced after exposure to freeze-thaw cycling for all composites, but the degree of these changes was dependent on the wood fibre source.     

Factorial study of material and process parameters on the mechanical properties of extruded kenaf fibre/polypropylene composite sheets

Thin kenaf/polypropylene (PP) composite sheets were manufactured via extrusion. The effects of kenaf and maleated PP (MAPP) proportions, fibre length, PP melt flow index (MFI) and die temperature on tensile, flexural, in-plane and out-of-plane shear properties were analysed by conducting experiments through ‘design of experiments’ methodology. Higher kenaf content and lower die/barrel temperatures resulted in composite sheets with higher average mechanical properties in various modes of testing. Matrix MFI appeared to significantly affect all mechanical properties. It is interesting to note that the properties of the very short-fibre composites produced are comparable to those reinforced with longer discontinuous fibres and long-fibre mats.     

Flexural behaviour of hybrid laminated composites

The present paper studies the flexural behaviour of hand manufactured hybrid laminated composites with a hemp natural fibre/polypropylene core and two glass fibres/polypropylene surface layers at each side of the specimen. When compared with full glass fibres reinforced polypropylene laminates, the hybrid composites have economical, ecological and recycling advantages and also specific fatigue strength benefits. Static and fatigue tests were performed in three point bending for both laminates to evaluate flexural strength properties and fatigue behaviour. Fatigue damage was measured in terms of the stiffness loss. Failure sites and mechanisms were evaluated through microscopy studies and a 3D numerical analysis using finite element method.