Melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites. I. Untreated fibers

The melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites was studied with an Instron capillary rheometer. The variation of melt viscosity with shear rate and shear stress at different temperatures was studied. The effect of relative composition of component fibers on the overall rheological behavior also was examined. A temperature range of 130 to 150°C and shear rate of 16.4 to 5470 s^?1 were chosen for the analysis. The melt viscosity of the hybrid composite increased with increase in the volume fraction of glass fibers and reached a maximum for the composite containing glass fiber alone. Also, experimental viscosity values of hybrid composites were in good agreement with the theoretical values calculated using the additive rule of hybrid mixtures, except at low volume fractions of glass fibers. Master curves were plotted by superpositioning shear stress and temperature results. The breakage of fibers during the extrusion process, estimated by optical microscopy, was higher for glass fiber than sisal fiber. The surface morphology of the extrudates was analyzed by optical and scanning electron microscopy. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 432–442, 2003     

Injection molding of long sisal fiber–reinforced polypropylene: Effects of compatibilizer concentration and viscosity on fiber adhesion and thermal degradation

A two‐step process was used to obtain long sisal fiber‐polypropylene (SF/PP)–reinforced thermoplastic composites, using maleic anhydride grafted polypropylene (MA‐g‐PP) as a compatibilizer. At a first stage, modified polypropylenes (mPP) were used for an extrusion impregnation process, for the preparation of composite pellets containing about 70 wt% of SF. SF/mPP pellets with a large aspect ratio were prepared by continuous extrusion impregnation of a continuous SF yarn, using a single screw extruder and an adequate impregnation die. The mPP used were MA‐g‐PP and regular polypropylene (PP), modified by reaction with different amounts of an organic peroxide. The composite pellets were thus dry blended with regular PP pellets in an injection machine hopper, and injection molded to obtain composite tensile specimens with a minimum quantity of modified polypropylene, minimum fiber breakage and thermal degradation, and excellent mechanical properties. It is shown that the fiber breakage is reduced to a minimum, even for recycled composites, due to the presence of the low‐viscosity polymer layer wetting the SF fibers. The bulk composite effective viscosity and the fiber breakage extent and thermal degradation during the injection‐molding step are found to be closely related. Blending with much less expensive mPP at the impregnation stage optimizes the amount of expensive MA‐g‐PP. POLYM. ENG. SCI., 45:613–621, 2005. © 2005 Society of Plastics Engineers     

Reinforcement of polypropylene using sisal fibers grafted with poly(methyl methacrylate)

Sisal fiber (SF) surface modification was carried out by grafting with methyl methacrylate (MMA) using cerium and ammonium nitrate as initiator. The effects of reaction time, monomer, and initiator concentration on the grafting parameters were systematically investigated. The results showed that MMA was successfully grafted onto the sisal fiber surface. The PMMA‐grafted sisal fibers were melt blended with polypropylene (PP) and then injection molded. The PP/SF composites were characterized by means of thermal analysis, mechanical testing, wide‐angle X‐ray diffraction, and SEM examination. PMMA grafted onto the surface of SF enhanced the intermolecular interaction between the reinforcing SF and PP matrix, improved the dispersion of SF in the PP matrix, and promoted the formation of β‐crystalline PP. These enhanced the thermal stability and mechanical properties of PP/SF composites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1055–1064, 2003     

Polyaniline–polypropylene melt‐spun fiber filaments: The collaborative effects of blending conditions and fiber draw ratios on the electrical properties of fiber filaments

A melt‐processable polyaniline complex was blended with polypropylene under different mixing conditions and melt‐spun into fiber filaments under different draw ratios. The conductivity, electrical resistance at different voltages, and morphological characteristics of the prepared fibers were investigated. The morphology of this two‐phase blend was demonstrated to have a large effect on the conductivity level and the linearity of the resistance–voltage relationship of the blend fibers. Two factors had substantial effects on the morphology and electrical properties of the fibers. They were the size of the initial dispersed conductive phase, which depended on the melt blending conditions, and the stress applied to orient this phase to a fibril‐like morphology, which was controlled by the draw ratio of the fiber. The two factors were shown to be associated with each other to maintain an appropriate balance of fibril formation and breakage and to create continuous conductive pathways. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structural properties and mechanical behavior of injection molded composites of polypropylene and sisal fiber

Composites based on isotactic polypropylene (PP) and sisal fiber (SF) were prepared by melt mixing and injection molding. The melt mixing characteristics, thermal properties, morphology, crystalline structure, and mechanical behavior of the PP/SF composites were systematically investigated. The results show that the PP/SF composites can be melt mixed and injection molded under similar conditions as the PP homo‐polymer. For the composites with low sisal fiber content, the fibers act as sites for the nucleation of PP spherulites, and accelerate the crystallization rate and enhance the degree of crystallinity of PP. On the other hand, when the sisal fiber content is high, the fibers hinder the molecular chain motion of PP, and retard the crystallization. The inclusion of sisal fiber induces the formation of β‐form PP crystals in the PP/SF composites and produces little change in the inter‐planar spacing corresponding to the various diffraction peaks of PP. The apparent crystal size as indicated by the several diffraction peaks such as L_(110)α, L_(040)α, L_(130)α and L_(300)β of the α and β‐form crystals tend to increase in the PP/SF composites considerably. These results lead to the increase in the melting temperature of PP. Moreover, the stiffness of the PP/SF composites is improved by the addition of sisal fibers, but their tensile strength decreases because of the poor interfacial bonding. The PP/SF composites are toughened by the sisal fibers due to the formation of β‐form PP crystals and the pull‐out of sisal fibers from the PP matrix, both factors retard crack growth.     

Melt rheological behavior of starch‐based matrix composites reinforced with short sisal fibers

A systematic analysis of the melt rheological behavior of a commercial starch‐based (MaterBi®) matrix composite reinforced with short sisal fibers is presented. The effects of shear rate, temperature, fiber content and treatment were analyzed by parallel‐plate rheometry, and classical non‐Newtonian models were applied to analyze the pseudoplasticity behavior of the molten composite systems. It is reported that shear rate is the most influential processing condition, while, from the point of view of the material structure, the intercalation effectiveness of the matrix in the fibers is directly linked to the rheological behavior. In fact, processing techniques with high stresses and more efficient mechanical mixing promote the opening of fiber bundles, increasing the aspect ratio of the fibers and the average viscosity of the molten composite. A similar effect on the increase of the aspect ratio and composite viscosity is observed when treated fibers are used. Polym. Eng. Sci. 44:1907–1914, 2004. © 2004 Society of Plastics Engineers.     

Effect of processing conditions on dimensions of sisal fibers in thermoplastic biodegradable composites

Biodegradable composites based on treated and untreated sisal fiber and mater Bi‐Z were processed using an internal batch mixer. The effect of processing conditions (temperature, speed of rotation, and time of mixing) and alkaline treatment on the dimensions of sisal fiber was studied. The length and diameter of the initial fibers were reduced during mixing and this effect was correlated to the magnitude of the shear stress developed in the mixer. An increase of the speed of rotation and/or a reduction of temperature produced fibers of smaller dimensions but with a higher aspect ratio l/d. Alkaline treatment increased the kinetics associated to the reduction of the fiber's dimensions. A semiempirical model was employed to predict the size of the fibers versus the time of mixing. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1084–1091, 2001     

Effect of alkali‐resistant glass fiber on polypropylene/polystyrene blends: Modeling and characterization

Alkali‐resistant glass fiber (GF) reinforced polypropylene (PP)/polystyrene (PS) blends were prepared by melt mixing in a Thermo Haake Rheochord mixer. Variation in thermal and mechanical properties with the addition of glass fibers into the polypropylene/polystyrene blends was investigated. The characterization of PP/PS/GF composites was done by dynamic mechanical analysis (DMA), thermogravimetric analysis, scanning electron microscope, and transmission electron microscope. The experimentally observed tensile properties of glass fiber reinforced PP/PS blends were compared with various published models. It was found that the experimental results agree well with Hui‐ Shia and series models. DMA tests revealed an increase in storage modulus with fiber loading confirms the greater degree of stress transfer from the matrix to the fiber. TEM micrographs reveal that the glass fibers are located at the interface between the blend components. POLYM. COMPOS., 37:398–406, 2016. © 2014 Society of Plastics Engineers     

Unsaturated polyester‐toughened epoxy composites: Effect of sisal fiber on thermal and dynamic mechanical properties

In the present study, the mechanical and thermal properties of sisal fiber‐reinforced unsaturated polyester (UP)‐toughened epoxy composites were investigated. The sisal fibers were chemically treated with alkali (NaOH) and silane solutions in order to improve the interfacial interaction between fibers and matrix. The chemical composition of resins and fibers was identified by using Fourier‐transform infrared spectroscopy. The UP‐toughened epoxy blends were obtained by mixing UP (5, 10, and 15 wt%) into the epoxy resin. The fiber‐reinforced composites were prepared by incorporating sisal fibers (10, 20, and 30 wt%) within the optimized UP‐toughened epoxy blend. Scanning electron microscopy was used to analyze the morphological changes of the fibers and the adhesion between the fibers and the UP‐toughened epoxy system. The results showed that the tensile and flexural strength of (alkali‐silane)‐treated fiber (30 wt%) ‐reinforced composites increased by 83% and 55%, respectively, as compared with that of UP‐toughened epoxy blend. Moreover, thermogravimetric analysis revealed that the (alkali‐silane)‐treated fiber and its composite exhibited higher thermal stability than the untreated and alkali‐treated fiber systems. An increase in storage modulus and glass transition temperature was observed for the UP‐toughened epoxy matrix on reinforcement with treated fibers. The water uptake behavior of both alkali and alkali‐silane‐treated fiber‐reinforced composites is found to be less as compared with the untreated fiber‐reinforced composite. J. VINYL ADDIT. TECHNOL., 23:188–199, 2017. © 2015 Society of Plastics Engineers     

Role of Cenosphere Addition on Dielectric Properties of Sisal Fiber-Polypropylene Composites

This research investigates the influence of addition of porous additives on dielectric constant of polypropylene. Composite composed of PP matrix with sisal fiber having cylindrical pores and cenospheres having spherical pore, presents low dielectric constant. A new relation concerning porosity is proposed by modifying the usual mixing rule to predict the dielectric constant of PP composite. This research presents the dielectric properties of sisal fiber-reinforced PP composites with and with out cenospheres. Treated and untreated cenospheres with different concentration were loaded in chopped sisal fiber-reinforced polypropylene. The loading of the polypropylene with the sisal fiber, increases the dielectric constant ε′ and improves the ac conductivity σ_ac. The effect of temperature on the dielectric spectrum of polypropylene composites was investigated in the frequency range ranging from 1–10 kHz. Sisal fiber-reinforced polypropylene composites having 20% sisal fiber with and without cenospheres were developed and electrical properties such as dielectric constant (?′), dissipation factor (tanδ) and ac conductivity (σ_ac) of these composites were determined. Dielectric constant, tan δ, and a.c. conductivity increases with increase in temperature at different frequencies.     

A low‐cost,low‐fiber‐breakage,injection molding process for long sisal fiber reinforced polypropylene

Composites of polypropylene (PP) and non‐treated sisal fiber (SF) were prepared in a non‐conventional two‐step process that offers significant advantages. Maleic anhydride–grafted polypropylene (MA‐g‐PP) was used as a coupling agent, to improve adhesion between the polar sisal fiber and the non‐polar polypropylene continuous matrix. At a first step, SF/MA‐g‐PP pellets with large aspect ratio and very high fiber content are prepared by extrusion impregnation and coating of a continuous SF yarn, followed by cooling and cutting. The composite pellets are thus dry blended with regular PP pellets in the injection machine hopper, and injected to obtain composite tensile specimens with a minimum quantity of expensive MA‐g‐PP, minimum fiber breakage and thermal degradation, and excellent mechanical properties. The SF/MA‐g‐PP pellets have a fiber content of 70% (w/w). The composite tensile specimens have final fiber contents ranging from about 3.5% to 24.5% (w/w). The PP tensile strength rises by about 44%. The tensile modulus increases by 126%, and the heat distortion temperature (HDT) is raised by about 35 K. FT‐IR spectroscopy and SEM micrographic observation show that the MA‐g‐PP is covalently bonded to SF through esterification. Besides the improvement in mechanical and thermal properties, costs are reduced because of the lower content of very expensive MA‐g‐PP, and the use of a single‐screw extruder at high production rates. Polym. Eng. Sci. 44:1766–1772, 2004. © 2004 Society of Plastics Engineers.     

Manufacture and properties of a structural synthetic polymer fiber‐containing nanoclay for concrete reinforcement

This study established the optimum conditions for structural synthetic polymer fiber manufacture to make a fiber having excellent tensile strength. Two polypropylene resins, differing in their melt indices, and four different draw ratio values were investigated, that is, 6, 7, 8, and 9, to establish which had the greatest influence on tensile strength. The tensile strength and the modulus of elasticity were measured for the manufactured fibers. In addition, nanoclay was added to polypropylene and polyolefin fibers to improve the mechanical properties of fiber‐reinforced cementitious composites. The optimum mixing ratio and draw ratio of the synthetic polymer fibers were established prior to nanoclay addition. Fiber mixing ratios (polypropylene:polyethylene) of 100:0, 90:10, and 85:15, a draw ratio of 8, and nanoclay additions of 1, 3, and 5 wt% were studied. The modulus of elasticity improved with nanoclay addition, while the tensile strength remained almost unchanged, except in the case of 100% polypropylene with 5 wt% nanoclay. POLYM. COMPOS., 34:1698–1709, 2013. © 2013 Society of Plastics Engineers     

Behavior of sisal fiber concrete cylinders externally wrapped with jute FRP

The use of environmentally friendly natural fibers as building materials is benefit to achieve a sustainable construction. This article performs a study on the use of natural jute fibers as reinforcement of concrete and natural sisal fibers in fiber reinforced polymer (FRP) composites as concrete confinement, i.e., sisal fiber reinforced concrete (SFRC) composite column wrapped by jute FRP (JFRP) (SFRC‐JFRP). Uniaxial compression test was conducted to assess the compression performance of the composite columns as axial structural member. A total of 24 specimens were tested. The effects of JFRP wrapping thickness and sisal fiber inclusion on the compressive performance of the composite columns were investigated. Results indicate that JFRP confinement significantly increases the compressive strength and ductility of both PC and SFRC with an increase in JFRP thickness. Besides, the inclusion of sisal fiber further enhances the strength as well as the efficiency of confinement under uniaxial compression. Also, the models for ultimate strength and ultimate strain of PC‐JFRP and SFRC‐JFRP are proposed. POLYM. COMPOS., 38:1910–1917, 2017. © 2015 Society of Plastics Engineers     

Structure–property relationship studies in amine functionalized multiwall carbon nanotubes filled polypropylene composite fiber

Amine functionalized multiwalled carbon nanotubes (a‐MWNT) based polypropylene (PP) composite fibers were prepared in the presence of polypropylene‐g‐maleic anhydride (PP‐g‐MA) by melt‐mixing followed by melt‐spinning with subsequent post‐drawing of the as‐spun fibers of varying draw ratio (DR). In order to enhance the interfacial interaction, a‐MWNT were utilized in combination with PP‐g‐MA during melt‐mixing. Fourier transform infrared spectroscopic analysis revealed the formation of imide bonds between MA functionality of PP‐g‐MA and amine functional group of a‐MWNT. Higher tensile properties of PP/a‐MWNT/PP‐g‐MA composite fibers were registered with varying DR of the as‐spun fiber. Orientation factors of a‐MWNT and PP chains along the fiber axis were correlated with the higher tensile modulus and tensile strength of PP/a‐MWNT/PP‐g‐MA composite fiber of varying DR. Crystallization studies indicated the role of hetero‐nucleating action of a‐MWNT in PP/a‐MWNT/PP‐g‐MA composite fiber. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Characterization of the weak link of wool fibers

The variance of fiber morphology along a fiber and the natural and artificial flaws in the fiber structure represent the primary reasons for the weak link of fibers. Accordingly, the fiber weak link can be divided into two types, that is, the geometrical thinnest part and the structural weak point. Scanning electron microscopic observation was used to characterize the morphological features of the fiber weak points whose forms are the normal thin sections, natural flaws, and artificial damage. Both the fiber profile morphology and the tensile behavior of wool fibers have been measured using a single‐fiber analyzer (SIFAN) and an optical microscope with a CCD camera plus an XQ‐1 fiber tensile tester (OM + XQ). The results from the SIFAN and OM+XQ methods indicate that the fibers breaking at their minimum diameters represent only one part of the broken fibers. The percentage of this kind of breakage is in the range of 40–60%. A new approach is presented to identify the weak‐point breakage relying on the fiber tensile behavior. The experimental results show that the probabilities of weak‐point, normal, and thinnest‐part breakage evaluated by these methods approximate 40, 60, and slightly more than 80%, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1206–1212, 2003     

Influence of fiber volume fraction and aspect ratio in resol–sisal composites

Vegetable fibers are being used as reinforcements in polymeric matrices with a wide variety of applications. Among these fibers, sisal is of particular interest due to the high impact strength and moderate tensile and flexural properties of its derivated composites. Because of its low cost and affinity, a phenol–formaldehyde resin, resol, has been selected as the matrix to obtain resol–sisal composites. The influence of fiber length and volume fraction on flexural properties has been studied. An optimum for the fiber length as well as for the fiber volume fraction was found. The improvement of the properties occurred up to a length of about 23 mm. The use of longer fibers lead to reduced properties because they tended to curl and bend during processing. Besides, actual composite densities were lower than theoretical ones mainly due to the presence of voids. This undesirable porosity produced a reduction in flexural properties at high fiber contents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2714–2722, 2003     

剑麻纤维与晶须混杂增强聚丙烯复合材料

采用熔融共混和注塑成型方法制得了剑麻短纤维(SF)和CaSO4晶须混杂增强聚丙烯(PP)复合材料，研究了复合材料的热性能、微观结构和力学性能。结果表明，晶须提高了复合材料的热稳定性，阻碍了PP的结晶，降低了复合材料中PP相的结晶度和结晶速率；SF和晶须提高了复合材料的模量和韧性，但由于混杂增强复合材料弱界面键合的制约，晶须的高强性能并没有在复合材料中充分表现出来。     

剑麻纤维增强聚丙烯复合材料的冲击特性研究

采用片状层压工艺制备了短切剑麻纤维(SF)／聚丙烯(PP)复合材料，用高级仪器化摆锤冲击试验机对复合材料的冲击过程进行了全面分析，并借助扫描电子显微镜对复合材料的冲击破坏断口进行观察。结果表明：当SF的长度为20mm、wpp=30％时，SF对PP的增韧效果最好。采用短切SF增强PP基体，可使复合材料断裂过程吸收的能量增加，裂纹扩展缓慢，断裂后期吸收能量增大。     

Effect of interface modification on the mechanical properties of polystyrene‐sisal fiber composites

The effect of interface modification on the mechanical (tensile, impact and flexural) properties of polystyrene–sisal fiber composites was investigated. The interface modification was performed by treatment of sisal fibers with benzoyl chloride, polystyrene maleic anhydride (PSMA), toluene diisocyanate (TDI), methyl triethoxy silane and triethoxy octyl silane. These interface modifications improve the compatibility of hydrophilic sisal fiber with a hydrophobic polystyrene matrix and change the tensile, impact and flexural properties of the composite, but to varying degrees depending on the fiber modification. The treated fibers were analyzed by spectroscopic techniques. Scanning electron microscopy was used to investigate the fiber surface, fiber pullout, and fiber‐matrix interface.     

Computer‐aided mathematical modeling and numerical simulation and theoretical analysis of the polypropylene polymer air drawing in spunbonding nonwoven process

In this article, as a nonlinear mathematical problem, the air‐drawing model and the air jet flow field model of the polymer during spunbonding process are also presented, because the continuous filament fiber not always occurs in the spunbonding process, therefore, there exists the filament fiber breakage, the broken fibers occur in the flow field of spunbonding process is a two‐phase flow problem, we suggested a new model called the sphere–spring model that can best described the broken fibers movement features. At the same time, the air‐drawing model of the polypropylene polymer in a spunbonding process is presented and solved by introducing the numerical computation results of the air jet flow field of aerodynamic device. The model's predictions of the filament fiber diameters, crystallinities, and birefringences are coincided well with the experimental data. The effects of the processing parameters on the filament fiber diameter are discussed. A lower polymer throughput rate, lower quench air temperature, higher polymer melt initial temperature, higher air initial temperature, higher air initial speed, medium smaller venturi gap, higher air suction speed, higher quench air pressure, higher air suction speed, higher extrusion temperature, higher quench air pressure, higher cooling air temperature, and so on can all produce finer filament fiber. The results show great prospects for this research in the field of computer‐assisted design of spunbonding technology. POLYM. ENG. SCI., 54:481–492, 2014. © 2013 Society of Plastics Engineers