Structure and Properties of Glass Fiber Reinforced Polypropylene/Liquid Crystal Polymer Blends

A liquid crystal polymer (LCP) was used to improve the physical properties of glass fiber reinforced polypropylene (GFRPP). The LCP was beneficial to improve the mechanical and heat resistant properties of the GFRPP/LCP composite. Compared with the GFRPP with 30% (w%) glass fiber (GF), the yield strength and the impact strength for the GFRPP/LCP composites increased by 62.7% and 18.1%, respectively, with a 6.8°C increase in the Vicat softening temperature for a 5% LCP addition to the GFRPP composites. The crystallinity of the polypropylene (PP) matrix for the GFRPP/LCP composites increased for 5% LCP and then decreased with increasing the LCP content. The γ-phase crystals for the PP matrix occurred in the shear layer of the injection molded GFRPP/LCP samples. The improved adhesion interface between the GF and the PP matrix was beneficial to reinforce and toughen the GFRPP/LCP composites with a small addition of the LCP.     

Fabrication of continuous fiber-reinforced thermoplastic composites with structural gradient from sheath-core type bicomponent fibers

Sheath-core type bicomponent fibers of polypropylene (PP) as a sheath component and thermotropic liquid crystalline polymer (TLCP) as a core component were prepared by the highspeed melt spinning process. Continuous fiber reinforced thermoplastic composites, in which TLCP acts as a reinforcing fiber and PP as a matrix polymer, were fabricated by the compression molding of these fibers. In the melt spinning, the attainable highest take-up velocity of TLCP was improved by co-processing with PP. Tensile modulus and strength of the TLCP component in the PP/TLCP bicomponent fibers increased with an increase in the take-up velocity. Comparison of wide-angle X-ray diffraction patterns of starting bicomponent fibers and fabricated composites indicated that the orientation relaxation of TLCP did not occur in the compression molding process. Accordingly, the tensile modulus and strength of the PP/TLCP composites were similar to those of the bicomponent fibers. Continuous fiber reinforced thermoplastic composites with various types of fiber content distributions were fabricated from the bicomponent fibers in which sheath-core composition was changed gradually in the spinning process. In the three-point bending test, the composites with two different types of symmetric structural gradients, one with higher TLCP fiber content near the surfaces than in the center and the other with higher TLCP content in the center than near the surfaces, exhibited different flexural moduli even though the overall TLCP contents were comparable. In the three-point bending test of a composite with asymmetric structural gradient, the yielding behavior and maximum flexural load varied depending on the direction of load application although the initial flexural moduli were similar.     

Short sisal fiber reinforced polypropylene composites: the role of interface modification on ultimate properties

Sisal fibers have been used for the reinforcement of polypropylene matrix. The compatibilization between the hydrophilic cellulose fiber and hydrophobic PP has been achieved through treatment of cellulose fibers with sodium hydroxide, isocyanates, maleic anhydride modified polypropylene (MAPP), benzyl chloride and by using permanganate. Various fiber treatments enhanced the tensile properties of the composites considerably, but to varying degrees. The SEM photomicrographs of fracture surfaces of the treated composites clearly indicated the extent of fiber–matrix interface adhesion, fiber pullout and fiber surface topography. Surface fibrillation is found to occur during alkali treatment which improves interfacial adhesion between the fiber and PP matrix. The grafting of the fibers by MAPP enhances the tensile strength of the resulting composite. It has been found that the urethane derivative of polypropylene glycol and cardanol treatments reduced the hydrophilic nature of sisal fiber and thereby enhanced the tensile properties of the sisal–PP composites, as evident from the SEM photomicrographs of the fracture surface. The IR spectrum of the urethane derivative of polypropylene glycol gave evidence for the existence of a urethane linkage. Benzoylation of the fiber improves the adhesion of the fiber to the PP matrix. The benzoylated fiber was analyzed by IR spectroscopy. Experimental results indicated a better compatibility between benzoylated fiber and PP. The observed enhancement in tensile properties of permanganate-treated composites at a low concentration is due to the permanganate-induced grafting of PP on to sisal fibers. Among the various treatments, MAPP treatment gave superior mechanical properties. Finally, experimental results of the mechanical properties of the composite have been compared with theoretical predictions.     

New Insight into the Interfacial Enhancement of Polypropylene Glass Fiber Composites via a Compatibilizer: The Role of Injection Screw Temperature

Polypropylene (PP)glass fiber (GF) composites modified by maleic anhydride-grafted polypropylene (MAH-g-PP) were prepared and the thermal influence on the interfacial properties was characterized and discussed. The results showed that the migration of MAH-g-PP from the PP matrix onto the GF surface was a thermally activated process. To be more specific, with the increasing processing temperature, more MAH-g-PP migrated onto the interface region to bridge PP matrix and GF together and promote the interfacial interaction, resulting in more efficient applied load transfer to GF through the interface. Accordingly, the mechanical properties of PPGF composites were improved with increasing processing temperature. Moreover, based on the content of MAH-g-PP on the surface of the GF and the mobility of MAH-g-PP in the PPGF composites, a temperature-dependent mechanism for the enhanced interface was proposed. We suggest this study not only provides a guide to adjust processing parameters to prepare high-performance PPGF composite, but also would be applicable for other immiscible systems.     

Effect of Fiber Surface Modification on the Interfacial and Mechanical Properties of Kenaf Fiber-Reinforced Thermoplastic and Thermosetting Polymer Composites

The surfaces of kenaf fibers were treated with three different silane coupling agents. 3-glycidoxypropyltrimethoxy silane (GPS), 3-aminopropyltriethoxy silane (APS), and 3-methacryloxypropyltrimethoxy silane (MPS). Among them, the most effective one for the property improvement was GPS when it was applied to the kenaf fiber surfaces at 0.5 wt%. Thermoplastic polypropylene (PP) and thermosetting unsaturated polyester (UPE) matrix composites with chopped kenaf fibers untreated and treated at different GPS concentrations from 0.1 wt% to 5 wt% were fabricated using compression molding technique. The present study demonstrates that the interfacial, flexural, tensile, and dynamic mechanical properties of both kenaf/PP and kenaf/UPE composites importantly depend on the GPS treatments done at different concentrations. The greatest property improvement of both thermoplastic and thermosetting polymer composites was obtained with the silane treatment at 0.5 wt% and the mechanical properties were comparable with E-glass composites prepared the same polymer matrix under the corresponding fiber length and fiber loading. The results also agreed with each other with regard to their interfacial shear strength, flexural properties, tensile properties, storage modulus, with support of fracture surfaces of the composites.     

Composites from Brazilian natural fibers with polypropylene: mechanical and thermal properties

Brazil has a well established ethanol production program based on sugarcane. Sugarcane bagasse and straw are the main by-products that may be used as reinforcement in natural fiber composites. Current work evaluated the influence of fiber insertion within a polypropylene (PP) matrix by tensile, TGA and DSC measurements. Thus, the mechanical properties, weight loss, degradation, melting and crystallization temperatures, heat of melting and crystallization and percentage of crystallinity were attained. Fiber insertion in the matrix improved the tensile modulus and changed the thermal stability of composites (intermediary between neat fibers and PP). The incorporation of natural fibers in PP promoted also apparent T _c and ΔH _c increases. As a conclusion, the fibers added to polypropylene increased the nucleating ability, accelerating the crystallization process, improving the mechanical properties and consequently the fiber/matrix interaction.     

Comparative experimental studies on the mechanical and degradation properties of natural fibers reinforced polypropylene composites

Coir/silk fiber-reinforced polypropylene (PP) based unidirectional composites (40 wt.%) were manufactured by compression molding. Coir/silk fibers and PP sheets were treated with ultraviolet radiation at different intensities and then composites were fabricated. It was found that mechanical properties of irradiated silk/irradiated PP composites were found to increase significantly compared to the untreated ones and even higher than that of irradiated coir/irradiated PP composites. Soil degradation tests indicated that irradiated coir/irradiated PP composites significantly lost much of its mechanical properties, but irradiated silk/irradiated PP composites retained their strength of its original integrity. Scanning electron microscopy and water uptake of both types of composites were also investigated.     

Modification of nano-kenaf surface with maleic anhydride grafted polypropylene upon improved mechanical properties of polypropylene composite

The surface of nano-kenaf fiber is modified with maleic anhydride grafted polypropylene (MA-g-PP) and added into PP and the mechanical properties and the flow property of the composite are investigated. The addition of MA-g-PP in nano-kenaf/PP composite increases the tensile strength, the elongation%, and the impact strength (I.S.), while it decreases the flow property (melt flow index) compared to without MA-g-PP composite (nano-kenaf/PP). The scanning electron microscope photograph shows it also increases interfacial adhesion between nano-kenaf and PP matrix. Regardless of MA-g-PP, nano-kenaf fibers shows better adhesion with PP compared to micron-kenaf fibers. Addition of MA-g-PP further improved interfacial adhesion between nano-kenaf surface and PP matrix compared to without MA-g-PP nano-kenaf compound. The addition of MA-g-PP apparently improves the interfacial adhesion between nano-kenaf surface and PP by formation of 3-dimensional network structure.     

Morphology,conductivity, and mechanical properties of polypyrrole-containing composites

An electrical-conducting polypropylene/polypyrrole (PP/PPy) composite was prepared by the chemically oxidative modification reaction of pyrrole on the surface of PP particles in suspension. Another type of PP/PPy composite was prepared by mixing the coated PP particles with noncoated PP particles at room temperature. The composites were processed by compression molding or by injection molding. The injection-molded composites exhibited better mechanical properties compared to compression-molded samples, while these composites showed better antistatic behavior and electrical conductivity. The differences in the behavior of the two types of composites were caused by the different structure of the PPy phase, which was studied by hot-stage optical microscopy and X-ray photoelectron spectroscopy (XPS).     

The Effects of Morphological Properties of Henequen Fiber Irradiated by EB on the Mechanical and Thermal Properties of Henequen Fiber/PP Composites

The aim of this study was to investigate the effects of electron beam (EB) irradiation on the morphological properties, crystallinity and surface area of henequen fiber and on the mechanical and thermal properties of henequen fiber reinforced polypropylene (PP) composites. The structure of henequen fiber was characterized by X-ray diffraction, mercury porosimetry and BET surface area analysis. The EB irradiation of 10 kGy led to the increasing of crystalline and surface pore area of henequen fiber, which contributed to the number of interlocking places with PP. From the results of tensile and impact strength tests, the highest value was observed for the composite reinforced with the henequen fiber treated with EB dose of 10 kGy, decreasing overall as EB dose increased. This tendency was also shown by coefficient of thermal expansion (CTE) measurements, but the value of CTE decreased until 50 kGy, meaning that a large total surface area can provide many interlocking places and so improve adhesion between fiber and matrix. Therefore, it can be concluded that the optimum pore surface area by 10 kGy irradiation contributes to successful mechanical interlocking between fiber and matrix and consequently enhances the mechanical and thermal properties of the composites.     

Effect of Interfacial Structure on Crystallization Behavior of Polypropylene/Polyolefin Elastomer/Barium Sulfate Ternary Composites

In this paper, interfacial structure induced development of crystallization behavior of polypropylene (PP)/polyolefin elastomer (POE)/barium sulfate (BaSO₄) ternary composites was studied by DSC. Two kinds of PP (copolymer and homopolymer) were used. The compatibility between PP and POE had a distinct influence on nucleation and crystal growth of PP in PP/POE binary composites. The crystallization rate of PP homopolymer increased because of the heterogeneous nucleation by POE, while the crystallinity of PP homopolymer decreased because of an inhibition effect of the hexane side chains in POE. BaSO₄ particles acted as heterogeneous nucleating agents of PP in ternary composites. The dispersion of BaSO₄, controlled by interfacial design, had a distinct influence on the nucleation activity of BaSO₄ in ternary composites. Interfacial structure had the same effect on nucleation activity of BaSO₄ particles and crystallization rate of PP matrix in PP copolymer ternary composites as those in PP homopolymer ternary composites.     

The thermal and thermomechanical behaviors of Spartium junceum flour reinforced polypropylene composites: effects of treatment and flour content

The effects of Spartium junceum (SJ) flour content, treatment time on the thermal and thermomechanical properties of polypropylene/Spartium junceum flour (PP/SJ) composites were studied. In order to improve the interfacial adhesion between the PP matrix and the SJ flour, SJ flour was treated with NaOH (2 wt%) for 8, 24 and 48 h at ambient temperature, respectively, and treated by vinyltrimethoxysilane (VTMS) (5 wt%). The results of thermogravimetric analysis (TGA) of SJ flour shows that the treatment improves the thermal stability of SJ flour. DSC analysis measurements illustrates that the addition of SJ flour increase the degree of crystallinity X_c, which indicate that the SJ flour plays a significant role in heterogeneous nucleating of PP matrix. The chemical treatments significantly affect the storage modulus of composite, where E′ increases for composites with treated flour in comparison to the untreated ones.     

Interphase sizing temperature effect of LaRC PETI-5 on the dynamic mechanical thermal properties of carbon fiber/BMI composites

The dynamic mechanical thermal properties of carbon fiber-reinforced bismaleimide (BMI) composites processed using polyacrylonitrile(PAN)-based carbon fibers unsized and sized with LaRC PETI-5 amic acid oligomer as interphase material at 150°C, 250°C, and 350°C were investigated by means of dynamic mechanical thermal analysis. It was found that the storage modulus, loss modulus, tan δ and the peak temperature significantly depend on the sizing temperature as well as on the presence and absence of LaRC PETI-5 sizing interphase. The result showed that the carbon fiber/BMI composite sized at 150°C had the highest storage modulus at a measuring temperature of 250°C. The storage modulus decreased with increasing sizing temperature from 150°C to 350°C, being influenced by interdiffusion and co-reaction between the LaRC PETI-5 interphase and the BMI matrix resin. The present result is quite consistent with the interfacial result reported earlier in term of interfacial shear strength and interlaminar shear strength of carbon fiber/BMI composites. It is addressed that in the present composite system the sizing temperature of LaRC PETI-5 interphase critically influences not only the interfacial properties but also the dynamic mechanical thermal properties and its control is also important.     

The Effects of Surface and Pore Characteristics of Natural Fiber on Interfacial Adhesion of Henequen Fiber/PP Biocomposites

The pore characteristics and morphological changes of henequen fiber after electron beam (EB) irradiation were studied, and their effects on interfacial adhesion between henequen fiber and polypropylene (PP) matrix of biocomposites were investigated. The surface morphologies of the fibers exposed to various EB irradiation doses were observed with an atomic force microscope (AFM). The porosity and pore distribution of fibers were characterized by mercury porosimetry and nonfreezing bound water (NFW) was measured by differential scanning calorimeter (DSC). Henequen fiber-reinforced polypropylene biocomposites were manufactured by the compression molding method and interlaminar shear strength (ILSS) was analyzed to examine the interfacial adhesion between henequen fiber and the PP matrix of the biocomposites. The AFM images indicated that pectin, waxy materials and impurities were removed from the surfaces of the henequen fibers during EB irradiation, resulting in changes of the surface morphology and characteristics of the fibers. When pectin, waxy compounds and impurities were removed, small pores of 1–0.01 μm were produced, and total surface area and porosity were increased. The increase in total surface area and porosity induced better adhesion between fiber and polymer which was confirmed by ILSS tests. However, the excessive creation of small pore size gives a negative effect on the tensile strength of henequen fiber. The best interfacial adhesion between henequen fiber and PP was obtained for the biocomposite reinforced with the henequen fiber treated with 10 kGy, which has the highest surface area and optimum pore diameter for interlocking between henequen fiber and polypropylene.     

Banana fiber/chemically functionalized polypropylene composites with in-situ fiber/matrix interfacial adhesion by Palsule process

Chemically functionalized maleic anhydride (MAH)-grafted polypropylene matrix has been used (in place of polypropylene as matrix with compatibilizer) to process banana fiber/chemically functionalized polypropylene (BF/CFPP) composites, without using any compatibilizer and without any fiber modification by Palsule process. Fiber/matrix interfacial adhesion generated, in-situ, due to interactions between BF and the MAH of the CFPP matrix has been established by Fourier transform infrared spectroscopy and scanning electron microscopy. Mechanical properties of the BF/CFPP composites developed by Palsule process with in-situ fiber/matrix interfacial adhesion in this study have been found to be higher than those of the matrix and it increases with increasing amounts of fibers in composites, and are better than properties of literature reported BF/polypropylene composites processed with compatibilizers. Measured modulus of BF/CFPP composites compares well with values predicted by rule of mixtures, Hrisch model, Halpin-Tsai equations and its modified Nielsen version, and with Palsule equation. The feasibility of developing natural fiber/MAH grafted polyolefin composites by Palsule process without using any compatibilizer and without any fiber treatment is demonstrated.     

The Preparation and Study on Ultrahigh Molecular Weight Polypropylene Gel‐spun Fibers

A novel polypropylene (PP) fiber was prepared by using gel spinning/crystallization from dilute solutions of ultrahigh molecular weight isotactic polypropylene (i‐UHMWPP), and subsequently drawing at various temperatures. The influence of drawing temperature on the properties of the resulted fibers was investigated. We found that the draw‐ability and mechanical as well as crystallization properties of the fibers obtained were dramatically improved with increasing drawing temperature. When the drawing temperature is below the α‐crystal relaxation temperature of PP, which was measured by wide‐angle X‐ray diffraction (WAXD) analysis as 100–120°C, the fibers are characterized by lower crystallinity and smaller crystals with less perfection, resulting in brittle fracture and subsequently poor mechanical durability. With drawing at temperatures above the α‐crystal relaxation temperature of PP, a novel UHMWPP fiber with Young's modulus of 27 GPa and tensile strength of 1.3 GPa was obtained. Higher crystallinity and larger crystals with better perfection and orientation were observed in this fiber.     

Relation between interfacial shear strength and compressive strength of carbon fiber/epoxy resin composite strands

The mechanism with which the fiber-matrix interfacial strength exerts its influence on the compressive strength of fiber reinforced composites has been studied by measuring the axial compressive strength of carbon fiber/epoxy resin unidirectional composite strands having different levels of interfacial shear strength. The composite strands are used for experiments in order to investigate the compressive strength which is not affected by the delamination taking place at a weak interlayer of the laminated composites. The interfacial strength is varied by applying various degrees of liquid-phase surface treatment to the fibers. The efficiency of the compressive strength of the fibers utilized in the strength of the composite strands is estimated by measuring the compressive strength of the single carbon filaments with a micro-compression test. The compressive strength of the composite strands does not increase monotonically with increasing interfacial shear strength but showes lower values at higher interfacial shear strengths. With increasing interfacial shear strength, the suppression of the interfacial failure in the misaligned fiber region increases the compressive strength, while at higher interfacial shear strengths, the enhancement of the crack sensitivity decreases the compressive strength.     

Investigation on Properties of Polypropylene/Multi-walled Carbon Nanotubes Nanocomposites Prepared by a Novel Eccentric Rotor Extruder Based on Elongational Rheology

The properties of polymer matrix composites are related not only to the chemical composition of the materials but also to the processing equipment used for their preparation which has a direct influence on the microstructure of the composites. In this paper polypropylene (PP)/multi-walled carbon nanotubes (MWCNTs) nanocomposites were prepared by melt blending through a self-developed, eccentric rotor extruder (ERE). The structure and elongational deformation mechanism of an ERE were described in detail. The morphological, rheological, thermal and mechanical properties of the resulting PP/MWCNTs nanocomposites were investigated. Scanning electron microscopy (SEM) and rheological analysis showed that the MWCNTs were well dispersed in the PP matrix. The thermal stability was investigated by thermogravimetric analysis (TGA) and indicated that the addition of MWCNTs could effectively improve the thermal stability of pure PP. The percentage of crystallinity and tensile strength of the composites were improved as a result of the heterogeneous nucleation effect of the MWCNTs in the PP matrix. The research results revealed that the enhancement of the properties of PP/MWCNTs composites could be attributed to a better dispersion of the MWCNTs in the matrix as compared to samples prepared by conventional extrusion.     

The effect of surface treatment of carbon fiber on the flexural property of thermoplastic polyimide composite

Rare earth solution (RES) surface modification and air-oxidation methods were used to improve the interfacial adhesion of the carbon fiber reinforced polyimide (CF/PI) composite. The flexural property of the PI composites reinforced by the carbon fibers treated with different surface modification methods was comparatively investigated. Results showed that the flexural strength of CF/PI composite was improved after RES treatment. The improvement of impact and flexural property of the CF/PI composite was mainly due to the improvement in interfacial adhesion after RES treatment. X-ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that the oxygen concentration was obviously increased after RES treatment. The increase in the amount of organic functional groups increased the interfacial adhesion between CF and PI matrix.     

Enhanced interfacial adhesion between PMMA and carbon fiber by graphene oxide coating

The purpose of this study is to increase the interfacial properties in PMMA/carbon fiber (PMMA/CF) composites Graphene oxide (GO) and brached polyethyleneimine were coated onto the surface of carbon fiber by layer-by-layer assembly in this work. Compared with the origin PMMA/CF composite, the composites reinforced by PMMA/CF–GO showed significant enhancement in interFacial shear strength (IFSS). The improved fiber–matrix adhesion was proved by fracture morphology observation of scanning electron microscopy and almost unaffected mechanical properties of the fiber itself during the coating process. The optimal assembly time was found to be 10 for enhancing the overall composite mechanical performance.