On the mechanism of polypropylene fibres in preventing fire spalling in self-compacting and high-performance cement paste

With the increasing application of self-compacting concrete (SCC) in construction and infrastructure, the fire spalling behavior of SCC has been attracting due attention. In high performance concrete (HPC), addition of polypropylene fibers (PP fibers) is widely used as an effective method to prevent explosive spalling. Hence, it would be useful to investigate whether the PP fibers are also efficient in SCC to avoid explosive spalling. However, no universal agreement exists concerning the fundamental mechanism of reducing the spalling risk by adding PP fiber. For SCC, the reduction of flowability should be considered when adding a significant amount of fibres.In this investigation, both the micro-level and macro-level properties of pastes with different fiber contents were studied in order to investigate the role of PP fiber at elevated temperature in self-compacting cement paste samples. The micro properties were studied by backscattering electron microscopy (BSE) and mercury intrusion porosimetry (MIP) tests. The modification of the pore structure at elevated temperature was investigated as well as the morphology of the PP fibers. Some macro properties were measured, such as the gas permeability of self-compacting cement paste after heating at different temperatures. The factors influencing gas permeability were analyzed.It is shown that with the melting of PP fiber, no significant increase in total pore volume is obtained. However, the connectivity of isolated pores increases, leading to an increase of gas permeability. With the increase of temperature, the addition of PP fibers reduces the damage of cement pastes, as seen from the total pore volume and the threshold pore diameter changes. From this investigation, it is concluded that the connectivity of pores as well as the creation of micro cracks are the major factors which determine the gas permeability after exposure to high temperatures. Furthermore, the connectivity of the pores acts as a dominant factor for temperatures below 300 °C. For higher temperatures micro cracks are becoming the major factor which influences the gas permeability.     

Performance of spalling resistance of high performance concrete with polypropylene fiber contents and lateral confinement

This paper presents an experimental study on the spalling resistance of high performance concrete with polypropylene (PP) fibers and fabric or sheet material for lateral confinement subjected to fire. According to the test results, spalling occurred on all specimens that did not contain PP fiber in the concrete mixture. However, spalling did not occur on specimens containing PP fibers above 0.05% by volume. A metal fabric showed beneficial effect on spalling resistance, but glass or carbon fiber fabrics do not show the same effect on the spalling resistance due to reduction of bond strength at high temperatures. Spalling did not occur on all specimens in which PP fibers and metal fabric were applied at the same time, and hence spalling resistance performance was significantly improved. The residual compressive strength was maintained at about 90% of its original strength, and this can be considered as an improved performance against fire damage.     

Parameter-study on the influence of steel fibers and coarse aggregate content on the fresh properties of self-compacting concrete

Self-compacting concrete (SCC) offers several economic and technical benefits; the use of steel fibers extends its possibilities. Steel fibers bridge cracks, retard their propagation, and improve several characteristics and properties of the concrete. Fibers are known to significantly affect the workability of concrete. Therefore, an investigation was performed to compare the properties of plain SCC and SCC reinforced with steel fibers. Two mixtures of SCC with different aggregate contents were used as reference. Each of the concretes was tested with four types of steel fibers at different contents in order to answer the question to what extent the workability of SCC is influenced. The slump flow, a fiber funnel and the J-ring test were used to evaluate the material characteristics of the fresh concrete. This paper discusses the suitability of the applied test methods and the effect of the coarse aggregate content, the content and type of steel fibers on the workability of SCC.     

Effect of maleic anhydride grafted polypropylene on the mechanical and morphological properties of chemically modified short‐pineapple‐leaf‐fiber‐reinforced polypropylene composites

With the rising cost of petroleum‐based fibers, the utilization of plant fibers in the manufacture of polymer–matrix composites is gaining importance worldwide. The scope of this study was to examine the perspective of the use of pineapple leaf fibers (PALFs) as reinforcements for polypropylene (PP). These fibers are environmentally friendly, low‐cost byproducts of pineapple cultivation and are readily available in the northeastern region of India. Here, both untreated and treated pineapple fibers were used. Maleic anhydride grafted polypropylene (MA‐g‐PP) was used as a compatibilizing agent. The polymer matrix of PP was used to prepare composite specimens with different volume fractions (5–20%) of fibers by the addition of 5% of MA‐g‐PP. These specimens were tested for their mechanical properties, and additional assessments were made via observations by scanning electron microscopy, thermogravimetric analysis, and IR spectroscopy. Increase in the impact behavior, flexural properties, and tensile moduli of the composites were noticed, and these were more appreciable in the treated fibers mixed with MA‐g‐PP. PALF in 10 vol % in PP mixed with MA‐g‐PP was the optimum and recommended composition, where the flexural properties were the maximum. The impact strength and the tensile modulus were also considerably high. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Rheological behavior of polyester blend and mechanical properties of the polypropylene–polyester blend fibers

The article deals with method of preparation, rheological properties, phase structure, and morphology of binary blend of poly(ethylene terephthalate) (PET)/poly(butylene terephthalate) (PBT) and ternary blends of polypropylene (PP)/(PET/PBT). The ternary blend of PET/PBT (PES) containing 30 wt % of PP is used as a final polymer additive (FPA) for blending with PP and subsequent spinning. In addition commercial montane (polyester) wax Licowax E (LiE) was used as a compatibilizer for spinning process enhancement. The PP/PES blend fibers containing 8 wt % of polyester as dispersed phase were prepared in a two‐step procedure: preparation of FPA using laboratory twin‐screw extruder and spinning of the PP/PES blend fibers after blending PP and FPA, using a laboratory spinning equipment. DSC analysis was used for investigation of the phase structure of the PES components and selected blends. Finally, the mechanical properties of the blend fibers were analyzed. It has been found that viscosity of the PET/PBT blends is strongly influenced by the presence of the major component. In addition, the major component suppresses crystallinity of the minor component phase up to a concentration of 30 wt %. PBT as major component in dispersed PES phase increases viscosity of the PET/PBT blend melts and increases the tensile strength of the PP/PES blend fibers. The impact of the compatibilizer on the uniformity of phase dispersion of PP/PES blend fibers was demonstrated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4222–4227, 2006     

Thermal stress–strain of self‐compacting concrete in compression

Self‐compacting concrete or self‐consolidation concrete (SCC) is being used in underground and other industrial structures that may be subjected to high temperatures during operation or in case of an accidental fire. The proper understanding of the effects of elevated temperatures on the stress–strain relationship of SCC is necessary in the assessment of structural safety. This paper presents the high temperature behavior from an experimental study carried out on SCC subjected to high temperatures. The effects of temperature, strength grade, and polypropylene (PP) fibers on the initial elastic modulus, strain at peak stress, and stress–strain curves of SCC are studied, which offered a test basis for estimating the deformation of SCC under high temperature. An empirical constitutive formula for the thermal stress–strain of SCC is developed on the basis of the deformation characteristics of PP fiber‐modified SCC. Copyright © 2012 John Wiley & Sons, Ltd.     

Mechanical improvement of concrete by irradiated polypropylene fibers

Fiber reinforced concrete (FRC) contains fibers physically mixed with gravel, sand, cement, and water. So far, adequate mechanical performance of FRC has been obtained at high cost and using complex technologies; important here is the geometry and surface characteristics of the polymers. We have modified polymeric‐fiber surfaces by using gamma radiation. Irradiated polypropylene (PP) fibers were submitted to 0, 5, 10, 50, and 100 kGy of gamma irradiation dosages. First, tensile strength of PP fibers was evaluated, and then fibers blended at 0, 1.0, 1.5, and 2.0% in volume with Portland cement, gravel, sand, and water. The highest values of compressive strength were obtained with irradiated‐fibers at 10 kGy and 1.5% in volume of fiber. The result is 101 MPa, as compared to 35 MPa for simple concrete without fibers. POLYM. ENG. SCI., 45:1426–1431, 2005. © 2005 Society of Plastics Engineers     

Use of preimpregnated sisal yarn in woven reinforced polypropylene sheets: Thermoformability and mechanical properties

Thermoplastic composites were made from polypropylene (PP) and long sisal fibers (SF) by using different processing techniques. Four sets of composites specimens were made with a 60/40 (wt/wt) SF/PP ratio: the first set was made by melt‐blending PP and SF and compression molding 2‐mm‐thick flat sheets; a second set was made by melt‐blending PP, SF, and maleic anhydride grafted polypropylene (MA‐g‐PP); the third set was made by compression molding knitted SF yarns, preimpregnated with PP, between PP sheets; the fourth set was also made by compression molding knitted SF yarns, preimpregnated with diluted MA‐g‐PP, between PP sheets. The bidirectional array of fibers, containing 60% of SF well‐impregnated with a small quantity of MA‐g‐PP, increases the flexural modulus by 600%, the tensile modulus by 475%, and the tensile strength by 300% compared with unfilled PP. The composites sheets were successfully thermoformed with small wall thickness reductions to obtain a three‐dimensional (3D) shape with very low forming energy, outstanding mechanical properties, and excellent surface finish. POLYM. ENG. SCI., 45:976–983, 2005. © 2005 Society of Plastics Engineers     

Physical modification of polypropylene. III. Novel morphology of polypropylene and poly(ethylene-co-vinyl alcohol) with epoxy blend fibers

In this study, the novel morphology of polypropylene (PP) and poly(ethylene-co-vinyl alcohol) (EVOH) blend fibers is described. More precisely, the blend fibers of PP–EVOH containing a small amount of EVOH (1, 3, 5, 7, and 9% by weight), with and without epoxy (1 wt %), have been melt-spun at a constant spinning velocity (500 m/min). For the as-spun fiber, both the initial modulus and the tenacity increased with the increase in the EVOH content. The blend fibers with three draw ratios (2, 3, and 4) drawn at room temperature. The scanning electron microscopic study showed that a draw ratio of 2 reveals little about the morphological changes, whereas a draw ratio of 4 showed a streak structure perpendicular to the fiber axis for PP–EVOH (91/9 wt %) blend fibers. In addition, epoxy (1 wt %) containing PP–EVOH (91/9 wt %) blend fiber showed latitudinal streaks. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1049–1057, 1999     

The influence of matrix viscosity on properties of polypropylene/polyaniline composite fibers—Rheological,electrical, and mechanical characteristics

Electrically conductive composites containing polypropylene (PP) and polyaniline (PANI) were prepared using PP with three different melt flow rates (MFRs) and a commercial PANI‐complex in proportions of 80% by weight and 20%, respectively. Composite blends were melt‐spun to fibers under different solid‐state draw ratios. Rheological studies of dynamic viscosity, as well as the storage modulus and loss modulus showed that the prepared PANI‐complex/PP blends exhibit different dynamic rheological behavior, depending on the PP used. This confirms the blends' morphological differences. PP matrix viscosity was found to play an important role in the electrical properties of the prepared fibers. Fibers prepared using the matrix with the lowest viscosity, showed a larger dispersed phase size in the cross‐sectional SEM micrographs, maximum conductivity observed at higher draw ratios and a more linear resistance–voltage relationship than those of the fibers prepared using the higher viscosity matrices. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of the length and the volume fraction of wavy steel fibers on the behavior of self-compacting concrete

Self-compacting concrete (SCC) is a highly workable concrete that fills formwork under its own weight (without any vibration or impact). It also passes easily through small spaces between reinforcement bars. The inclusion of fibers in such concrete limits the concrete shrinkage cracks at early age and enhances some of its properties. However, fibers may affect the flow characteristics of SCC. In this paper, three wavy steel fibers (SF) of different lengths, 35, 40, and 50 ± 2 mm with six different volume fractions (V_f) of 0.3, 0.5, 0.8, 1, 1.2, and 1.4% were used in SCC. The experimental results showed that the addition of SF with higher V_f content and longer length decreases the workability of SCC, reduces its passing ability and increases the possibility of blockage. Mechanical performances of concrete in terms of flexural strength and elasticity modulus were improved, where the slightly compressive strength decreased with an increase in V_f content of SF.     

Study on depositing SiO2 nanoparticles on the surface of jute fiber via hydrothermal method and its reinforced polypropylene composites

To improve the interfacial compatibility of jute fiber reinforced polypropylene (PP) composites, hydrothermal method was used to deposit SiO₂ nanoparticles on the surface of pretreated jute fibers and the effect of reaction factors (tetraethoxysilane [TEOS] concentration, ammonia concentration, and reaction temperature) on the deposition of SiO₂ nanoparticles were evaluated. The results of FTIR, XRD, SEM, and TEM showed that the amorphous SiO₂ nanoparticles with an average particle size of 65.0 nm were successfully deposited on the surface of jute fibers at the TEOS/H₂O volume ratio of 1:2, ammonia of 0.55 M, reaction temperature of 100 °C (0.15 MPa) for 5 h. Compared with the sol–gel method, SiO₂ nanoparticles obtained by the hydrothermal method possessed smaller particle size and were less agglomerated, which can better fill in the surface defects of the jute fibers and result in a 12.9% increase in the tensile strength. The study on the mechanical properties and interface performance of the jute fiber reinforced PP composites indicated that the interfacial compatibility between jute fibers and PP was obviously improved. The tensile and impact strength of the composites reinforced with nano‐SiO₂ deposited jute fibers were increased by 26.87% and 25.65%, respectively, compared with the untreated jute fibers. J. VINYL ADDIT. TECHNOL., 26:43–54, 2020. © 2019 Society of Plastics Engineers     

Shrinkage of short PP and PAN fibers under hot-stage microscope

Marked shrinkage behavior when heated is typical of semicrystalline polymer fibers such as polypropylene (PP) and polyacrylonitrile (PAN). Shrinkage of PP and PAN fibers may give the possibility to control the spalling tendency of fiber concrete under the heat exposure of fire. Cut staple fibers are normally delivered for concrete reinforcement. Modern methods for continuous fibers cannot be used by the end-user for shrinkage determination of commerical staple fiber grades. The shrinkage of five different commercial staple fibers specially designed for concrete reinforcement was studied under a hot-stage microscope. Significant differences in cumulative shrinkages of the various PP and PAN fibers were detected, shrinkages being 3–15% with PP fibers and 6–7% with PAN fibers at a temperature of 150–170°C. At about 160–165°C, PP fibers melt, whereas PAN fibers continue shrinking. Hot-stage microscopy provides a simple and a relatively accurate method for estimating thermal shrinkage of staple PP and PAN fibers, the deviations from measured average values remaining typically at 10–15%. © 1995 John Wiley & Sons, Inc.     

Preparation and characterization of hydrophilicity fibers based on 2-(dimethyamino)ethyl mathacrylate grafted polypropylene by UV- irradiation for removal of Cr(VI) and as(V)

The hydrophilic fibers based on 2-(dimethylamino)ethyl methacrylate (DMAEMA) which could remove Cr(VI) ions rapidly were prepared by UV-irradiation induced grafting of DMAEMA through pre-coating photoinitiator on the fibers and modifying with bromoethane(BE). The FTIR, FESEM, XPS, TG-DTG and contact angle spectra manifested that DMAEMA was grafted onto the surface of PP fibers and subsequently was quaternized. The maximum grafting degree (22.9 %) and exchange capacity of DMAEMA (1.2 mmol g^?1) was obtained when PP fibers was immersed in BP concentration of 0.3 % for 4 h, irradiated with the DMAEMA concentration of 100 % and irradiation time of 20 min, and then was modified with BE. The modified fibers of PP-g-DMAEMA with bromoethane were proved to remove Cr(VI) and As(V) with removal rate of 97.3 % and 96.2 % within 10 min, respectively. The prepared fibers have potential application for the removal of Cr(VI) and As(V) from wastewater highly and rapidly.     

Preparation and characteristics of composites of high‐crystalline cellulose with polypropylene: Effects of maleated polypropylene and cellulose content

Binary composites of high‐crystalline fibrous cellulose with polypropylene (PP) or maleic anhydride‐grafted polypropylene (MAPP) were prepared by melt‐mixing with different contents of cellulose from 0 to 60 wt %. Ternary composites of cellulose with PP and MAPP were also prepared to investigate the effects of MAPP as a compatibilizer between cellulose and PP. Scanning electron microscopy revealed that the addition of MAPP generates strong interactions between a PP matrix and cellulose fibers: All cellulose fibers are encapsulated by layers of the matrix and connected tightly within the matrix. Thus, the tensile strength and Young's modulus of MAPP‐containing composites increase with an increase in MAPP and cellulose content, in contrast to the decrease in tensile strength of a PP‐based binary composite with an increase in cellulose. Cellulose fibers act as a nucleating agent for the crystallization of PP, which is promoted by the addition of MAPP through an increase of the crystallization temperature of PP in the composite. Accordingly, both cellulose and MAPP facilitate the thermooxidative stability of PP composites in the following order: MAPP/cellulose > PP/MAPP/cellulose > PP/cellulose > PP. Relative water absorption increases with an increase in cellulose content, decreasing with the addition of MAPP. MAPP‐containing cellulose composites have high potential for applications as environmentally friendly materials. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 337–345, 2003     

Mechanical properties of hybrid fiber-reinforced concrete at low fiber volume fraction

Concretes containing different types of hybrid fibers at the same volume fraction (0.5%) were compared in terms of compressive, splitting tensile, and flexural properties. Three types of hybrid composites were constructed using fiber combinations of polypropylene (PP) and carbon, carbon and steel, and steel and PP fibers. Test results showed that the fibers, when used in a hybrid form, could result in superior composite performance compared to their individual fiber-reinforced concretes. Among the three types of hybrids, the carbon-steel combination gave concrete of the highest strength and flexural toughness because of the similar modulus and the synergistic interaction between the two reinforcing fibers.     

Reinforcement of polypropylene with lignocellulose nanofibrils and compatibilization with biobased polymers

Freeze‐dried and milled lignocellulose nanofibrils (LCNF) were used to reinforce polypropylene (PP) nanocomposites. The LCNF, containing up to 9% lignin, was obtained from residual Empty Palm Fruit Bunch (EPFB) fibers. Soy protein isolate (SPI) and hydroxypropyl cellulose (HPC) were tested as coupling agents as well as maleic anhydride grafted polypropylene (MAPP), which was used as a reference. A good level of dispersion of LCNF in the PP matrix while mechanical testing and thermal analyses indicated an improvement of the thermo‐mechanical behavior of the nanocomposites was revealed upon loading of the lignin‐containing nanofibrils. The tensile modulus of PP was increased by 15% upon the addition of 1% LCNF with SPI as a compatibilizer. Likewise, the thermal stability of the composites was most markedly enhanced. Overall, LCNF and SPI, two important bioresources, are introduced here for the development of novel and cost‐effective PP‐based composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43854.     

聚丙烯/无机粉体/异形纤维复合材料的制备

以聚丙烯为聚合物基体,以纳米碳酸钙为无机组分,采用聚对苯二甲酸乙二醇酯(PET)纤维,纤维截面形状分别为圆形、扁平形和三角形,通过熔融共混的方法制备了聚丙烯/纳米碳酸钙/异形纤维复合材料,并采用不同的改性剂对纳米碳酸钙进行表面改性,通过扫描电子显微镜观察了纳米碳酸钙的分散情况,重点分析了聚丙烯/纳米碳酸钙/异形纤维复合材料的结构与性能的关系。结果表明,硅烷偶联剂对碳酸钙表面有机化处理的效果好于硬脂酸;纤维截面形状不同对复合材料的增强效果也不同,其中比表面积最大的三角形纤维增强效果最佳;当纳米碳酸钙的含量为3%(质量分数,下同)(2%硅烷偶联剂处理)、三角形PET纤维的长径比为80、含量为2%(体积分数,下同)(4%硅烷偶联剂处理)时,制得的聚丙烯/纳米碳酸钙/异形纤维复合材料的屈服强度比纯聚丙烯提高近21%,弹性模量提高了约82%。     

Polypropylene composites reinforced with untreated and chemically treated coir: Effect of the presence of compatibilizer

The effect of coir surface modification on the compatibility of polypropylene (PP)/coir fiber (CF) composites, in the presence and absence of compatibilizer (maleic anhydride grafted polypropylene, PP‐g‐MA) was assessed. Chemical pulping of the fibers was performed with 2, 4, 8, and 12% NaOH solutions for a period of 2 h at (100 ± 4)°C. Pressed composite samples were subjected to tensile testing, scanning electron (SEM) and atomic force microscopy (AFM). Lignin and holocellulose concentrations of untreated and treated coir were determined. Pulping resulted in increased tensile strength of the composites containing coir treated with up to 2% NaOH, due to increased fiber roughness as evidenced by AFM. This property decreased when higher NaOH concentrations were used, likely due to increased deterioration of coir. The presence of compatibilizer in the PP composites containing treated coir altered adhesion due to chemical changes of the fiber surface. At high NaOH concentrations increased delignification and therefore increased exposure of hydroxyls favors reaction between the fiber hydroxyls and the carboxyl acids of the hydrolyzed maleic anhydride, present in the composites. POLYM. ENG. SCI., 55:2050–2057, 2015. © 2014 Society of Plastics Engineers     

Moisture uptake and hygroexpansion of wood fiber composite materials with polylactide and polypropylene matrix materials

Effects of butantetracarboxylic acid (BTCA) modification, choice of matrix, and fiber volume fraction on hygroexpansion of wood fiber composites have been investigated. Untreated reference wood fibers and BTCA‐modified fibers were used as reinforcement in composites with matrices composed of polylactic acid (PLA), polypropylene (PP), or a mixture thereof. The crosslinking BTCA modification reduced the out‐of‐plane hygroexpansion of PLA and PLA/PP composites, under water‐immersed and humid conditions, whereas the swelling increased when PP was used as matrix material. This is explained by difficulties for the BTCA‐modified fibers to adhere to the PP matrix. Fiber volume fraction was the most important parameter as regards out‐of‐plane hygroexpansion, with a high‐fiber fraction leading to large hygroexpansion. Fiber‐matrix wettability during processing and consolidation also showed to have a large impact on the dimensional stability and moisture uptake. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers