Influence of two carbon plies on adhesion of unidirectional flax‐fibers reinforced epoxy composites

In this work, we undertook a comparative study of the dynamic dielectric analysis of two unidirectional epoxy composites: flax‐fiber‐reinforced epoxy and flax/carbon‐fiber‐reinforced epoxy (FCFRE). In both composites, three relaxation processes were identified. The first one is the water dipoles polarization imputed to the presence of polar water molecules in flax fiber. The second relaxation process associated with conductivity occurs as a result of the carriers charges diffusion noted for high temperature above glass transition and low frequencies. As for the third dielectric relaxation associated with the interfacial polarization effect is attributable to the accumulation of charges at the fibers/matrix interface. The presence of two carbon plies in the reinforcement gives rise to two interfacial polarization effects in the FCFRE composite. The analysis of the Maxwell–Wagner–Sillars and the water dipoles polarizations using the Havriliak–Negami model revealed that the presence of two plies of carbon can locally decrease the adhesion of flax fibers in the matrix. This analysis was supported by the thermal properties using a differential scanning calorimety and the mechanical properties using a short beam shear test. POLYM. COMPOS., 241–253, 2016. © 2014 Society of Plastics Engineers     

Study on interfacial properties of unidirectional flax/vinyl ester composites: Resin manipulation on vinyl ester system

Flax fibers are widely used as reinforcements in bio‐based polymer matrix composites. This study investigated the hydrophilic nature and surface purity of flax fiber that affects fiber/matrix adhesion in combination with hydrophobic structural polymers via matrix modification and the utilization of fiber treatment, specifically in a flax/vinyl ester (VE) composite. A new method to manipulate the vinyl ester system with acrylic resin (AR) was developed to produce flax reinforced. On the other hand, different types of chemical and physical treatments were applied on the flax fiber. FTIR was applied to evaluate the effects of surface treatments. Dynamic mechanical analysis (DMA) was used to analyze the unmodified and modified VE resin system. The surface of untreated and treated flax fibers and their composites were analyzed by scanning electronic microscopy (SEM). Sodium ethoxide‐treated flax/VE with 1% (wt) AR caused the best mechanical performance among all the flax/VE composites evaluated. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of macromolecular coupling agent on the property of PP/GF composites

Silane‐grafted polypropylene manufactured by a reactive grafting process was used as the coupling agent in polypropylene/glass‐fiber composites to improve the interaction of the interfacial regions. Polypropylene reinforced with 30% by weight of short glass fibers was injection‐molded and the mechanical behaviors were investigated. The results indicate that the mechanical properties (tensile strength, tensile modulus, flexural strength, flexural modulus, and Izod impact strength) of the composite increased remarkably as compared with the noncoupled glass fiber/polypropylene. SEM of the fracture surfaces of the coupled composites shows a good adhesion at the fiber/matrix interface: The fibers are coated with matrix polymer, and a matrix transition region exists near the fibers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1537–1542, 1999     

Unidirectional hemp and flax EP‐ and PP‐composites: Influence of defined fiber treatments

In some technical areas, mainly in the automotive industry, glass fiber reinforced polymers are intended to be replaced by natural fiber reinforced polymer systems. Therefore, higher requirements will be imposed to the physical fiber properties, fiber‐matrix adhesion, and the quality assurance. To improve the properties of epoxy resins (EP) and polypropylene (PP) composites, flax and hemp fibers were modified by mercerization and MAH‐PP coupling agent was used for preparing the PP composites. The effects of different mercerization parameters such as concentration of alkali (NaOH), temperature, and duration time along with tensile stress applied to the fibers on the structure and properties of hemp fibers were studied and judged via the cellulose I–II lattice conversion. It was observed that the mechanical properties of the fibers can be controlled in a broad range by using appropriate mercerization parameters. Unidirectional EP composites were manufactured by the filament winding technique; at the PP matrix material, a combination with a film‐stacking technique was used. The influence of mercerization parameters on the properties of EP composites was studied with hemp yarn as an example. Different macromechanical effects are shown at hemp‐ and flax‐PP model composites with mercerized, MAH‐PP‐treated, or MAH‐PP‐treated mercerized yarns. The composites' properties were verified by tensile and flexural tests. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2150–2156, 2004     

Surface Characterization of Differently Pretreated Flax Fibers and Their Application in Fiber-Reinforced Composites

Strong natural bast fibers, especially flax fibers, can be used to replace glass fibers in reinforced composites. The properties of natural fibers depend largely on maturity, retting and processing. Two chemical treatments were applied to retted and semiretted flax fibers to create better fiber to resin bonding and to show the effect of retting degree and successive purification processes on the mechanical properties of natural composite materials. Retted and semiretted flax fibers have been scoured and bleached with the objective of removing surface impurities and developing finer structure. To investigate the effect of adhesion promoter on the mechanical properties of natural fiber composite, a composite sample was prepared from bleached retted flax pretreated with adhesion promoter Isostearoyltitanate (ISTT).

After treatments the fibers got cleaner and the measurements showed that the fiber fineness as well as the surface free energy increased. The treatments were accompanied by decrease in the fiber tenacity but it has been found not to be reflected to the final mechanical properties of the composite. No improvement was remarked by using Isostearoyltitanate for surface modification.     

A review on interface modification and characterization of natural fiber reinforced plastic composites

An Important aspect with respect to optimal mechanical performance of fiber reinforced composites in general and durability in particular is the optimization of the interfacial bond between fiber and polymer matrix. The quality of the fiber‐matrix interface is significant for the application of natural fibers as reinforcement for plastics. Since the fibers and matrices are chemically different, strong adhesion at their interfaces is needed for an effective transfer of stress and bond distribution throughout an Interface. A good compatibilization between cellulose fibers and non‐polar matrices is achieved from polymeric chains that will favor entanglements and interdiffiusion with the matrix. This article gives a critical review on the physical and chemical treatment methods that improve the fiber‐matrix adhesion and their characterization methods.     

Influence of the fiber surface properties on the mechanical strength of unidirectional fiber composites

The influence of the thermodynamic adhesion between fibers and matrix on the mechanical properties of a continuous fiber reinforced composite is studied for two systems: carbon fiber reinforced poly(ether ether ketone) and glass fiber reinforced poly(ether imide). The fibers are modified chemically and characterized by measuring the contact angle formed by molten resin on the fibers. Various fiber treatments yield a wide range of contact angles, which are determined optically. Unidirectional fiber reinforced laminates are manufactured and transverse flexural strength is measured with the values reported as a function of the specific work of adhesion. It is shown that adhesion at the fiber-resin interface correlates with both the composite strength and the void morphology within the laminate after consolidation.     

Mechanical properties of glass/flax hybrid composites based on a novel modified soybean oil matrix material

In the Affordable Composites from Renewable Resources (ACRES) program at the University of Delaware, soybean oil and other plant triglycerides have been made amenable to polymerization using a broad range of chemical routes. The resultant polymers range in properties from soft rubbers to hard thermosets for composite applications. In this paper we present an investigation of the mechanical properties of glass/flax hybrid composites based on these thermoset matrix materials. Composites with different glass/flax ratios and different fiber arrangements were made using a modified soybean oil matrix material. The fiber arrangement was varied to make symmetric and unsymmetric composites. The latter were tested in different modes in flexural tests and drop weight impact tests. The mechanical properties of the composites were found to depend upon the glass/flax ratio and the arrangement of fibers in the composite. On proper selection of the arrangement of fibers in the composite, the glass fibers and flax fibers were found to act synergistically resulting in an improved flexural and impact performance. POLYM. COMPOS., 26:407–416, 2005. © 2005 Society of Plastics Engineers     

Use of silanes and copolymers as adhesion promoters in glass fiber/polyethylene composites

Two organofunctional silanes and three functionalized copolymers were used as adhesion promoters in glass fiber/polyethylene‐reinforced composites. The performance of the coupling agents was investigated by mechanical property measurements, scanning electron microscopy, and dynamic mechanical analysis. Coupling achieved with the poly(ethylene‐g‐maleic anhydride) copolymer proved to be the most successful compared with the other copolymers (ethylene/vinyl alcohol, ethylene/acrylic acid) and silane agents (γ‐methacryloxypropyltrimethoxy, cationic styryl). The combined coupling performance of the silanes and copolymers examined in this study appears to be controlled by the coupling performance of the copolymer. Effective coupling was reflected in increased mechanical properties. Increased fiber/matrix adhesion is not always associated with effective coupling because structural changes occurring at the interface region can result in a deterioration of the material property. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2877–2888, 2001     

Structural degradation and mechanical fracture of hybrid fabric reinforced composites

This investigation involves the study of accelerated environmental aging in two polymer composite laminates reinforced by hybrid fabrics based on carbon, Kevlar and glass fibers. Composite laminate configurations are defined as a laminate reinforced with E‐glass fiber and Kevlar 49 fiber hybrid fabric (GK) and another laminate reinforced with E‐glass fiber and AS4 carbon fiber hybrid fabric (GC). Both laminates were impregnated with epoxy vinyl ester thermosetting resin (Derakane 470‐300) consisting of four layers. Morphological studies (photo‐oxidation process and structural degradation) of environmental aging were conducted, in addition to comparative studies of the mechanical properties and fracture characteristics under the action of uniaxial tensile and three‐point bending tests in specimens in the original and aged conditions. With respect to uniaxial tensile tests for both laminates, good mechanical performance and little final damage (small loss of properties) was caused by the aging effect. However, for the three‐point bending tests, for both laminates, the influence of aging was slightly higher for all parameters studied. The low structural deterioration in the laminates is attributed to the high performance with the heat of the matrix (Derakane 470‐300) and the characteristics of the hybrid fabric, exhibiting fiber/matrix interface quality. POLYM. ENG. SCI., 56:657–668, 2016. © 2016 Society of Plastics Engineers     

Synthesis and characterization of short Grewia optiva fiber‐based polymer composites

Natural fibers, such as Flax, Sisal, Hibiscus Sabdariffa, and Grewia optiva (GO) possess good reinforcing capability when properly compounded with polymers. These fibers are relatively inexpensive, easily available from renewable resources, and possess favorable values of specific strength and specific modulus. The mechanical performance of natural fiber‐reinforced polymers (FRPs) is often limited owing to a weak fiber‐ matrix interface. In contrast, urea–formaldehyde (UF) resins are well known to have a strong adhesion to most cellulose‐containing materials. This article deals with the synthesis of short G. optiva fiber‐reinforced UF polymer matrix‐based composites. G. optiva fiber‐reinforced UF composites processed by compression molding have been studied by evaluating their mechanical, physical, and chemical properties. This work reveals that mechanical properties such as: tensile strength, compressive strength, flexural strength, and wear resistance of the UF matrix increase up to 30% fiber loading and then decreases for higher loading when fibers are incorporated into the polymer matrix. Morphological and thermal studies of the matrix, fiber, and short FRP composites have also been carried out. The swelling, moisture absorbance, chemical resistance, and water uptake behavior of these composites have also been carried out at different intervals. The results obtained lay emphasis on the utilization of these fibers, as potential reinforcing materials in bio‐based polymer composites. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Performance of fibers embedded in a cementitious matrix

Reinforcement of cementitious materials with short fibers has been proved to be an economical and effective way to convert these brittle materials to ductile products. Many fibers with different geometries have been used as reinforcement materials. Fibers bonding to cementitious materials play an important role in mechanical performance of these composites. This article describes the performance of (homemade) fibers as reinforcement in cement‐based materials by investigation on bonding characteristic of fiber to cement matrix. To this end, the fibers (glass, polypropylene, polyacrylonitrile (PAN), and high strength nylon 66 (N66)) are characterized using microscopy analysis, tensile strength, and alkali attack tests. The fibers embedded in the cement matrix, then, pulled‐out to evaluate their bonding to cementitious materials. SEM analysis is used to study fiber/cement interfacial transition zone. The results show that PAN fibers have the advantages of preparing for cementitious reinforcement. It was found that the reinforcing efficiency of fibers‐reinforced cementitious composites was strongly depending on interfacial contact area in fiber/matrix interface and chemical/physical properties of fibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

High Stiffness Natural Fiber‐Reinforced Hybrid Polypropylene Composites

Abstract

Natural fibers are potentially a high‐performance non‐abrasive reinforcing fiber source. In this study, pulp fibers [including bleached Kraft pulp (BKP) and thermomechanical pulp (TMP)], hemp, flax, and wood flour were used for reinforcing in polypropylene (PP) composite. The results show that pulp fibers, in particular, TMP‐reinforced PP has the highest tensile strength, possibly because pulp fibers were subjected to less severe shortening during compounding, compared to hemp and flax fiber bundles. Maleic‐anhydride grafted PP (MAPP) with high maleic anhydride groups and high molecular weight was more effective in improving strength properties of PP composite as a compatiblizer. Coupled with 10% glass fiber, 40% TMP reinforced PP had a tensile strength of 70 MPa and a specific tensile strength comparable to glass fiber reinforced PP. Thermomechanical pulp was more effective in reinforcing than BKP. X‐ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) were used to aid in the analysis. Polypropylene with high impact strength was also used in compounding to improve the low‐impact strength prevalent in natural fiber‐reinforced PP from injection molding.     

环氧改性聚碳酸酯单向纤维复合材料研究

采用Ｅ－５１环氧树脂改性聚碳酸酯，研究其单向Ｅ－玻璃纤维、单向碳纤维Ｔ３００、Ｍ４０复合材料。结果表明，改性后的聚碳酸酯复合材料（ＰＣＣＭ）的层间剪切强度等性能明显提高，玻纤复合材料提高幅度最大。纤维－基体界面粘接良好。     

亚麻纤维增强热固性树脂复合材料板材的研究

本文以亚麻纤维作为原料,经过针刺工艺制得亚麻纤维针刺毡,作为复合材料的增强体.通过改变纤维、热固性树脂种类,利用真空辅助RTM方法及模压法制备复合材料板材.对板材进行了拉伸及弯曲性能测试,比较了不同纤维和树脂的结合情况,进一步阐述了板材破坏机理.     

Sulphur‐vulcanized polybutadiene as a matrix in glass fiber‐reinforced composite materials

The basic material used in this work was a low‐molecular‐weight polybutadiene with isocyanate endgroups in the main chain. The isocyanate groups were used for crosslinking of the oligomeric polybutadiene with glycerol as a three‐functional crosslinker. The prepared polybutadiene‐based polyurethane gel was subsequently vulcanized with sulphur. The effect of sulphur content on mechanical and electrical properties of resulting materials was investigated with the aim to find an optimum matrix composition for the preparation of composite materials. Several types of glass fiber fabric reinforcement differing in fabric weight and fabric ply thickness were tested. Mechanical properties of composites based on the optimum matrix composition and different types of glass fibers were measured and compared. Being vulcanized with sulphur, the polybutadiene was found to possess improved mechanical properties and retain an excellent electroinsulating character. Moreover, the sulphur‐vulcanized polybutadiene was proved good as a matrix for the preparation of glass fiber‐reinforced composite materials having enhanced tensile and flexural properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Progress Report on Natural Fiber Reinforced Composites

This century has witnessed remarkable achievements in green technology in material science through the development of natural fiber reinforced composites. The development of high‐performance engineering products made from natural resources is increasing worldwide day by day. There is increasing interest in materials demonstrating efficient use of renewable resources. Nowadays, more than ever, companies are faced with opportunities and choices in material innovations. Due to the challenges of petroleum‐based products and the need to find renewable solutions, more and more companies are looking at natural fiber composite materials. The primary driving forces for new bio‐composite materials are the cost of natural fibers (currently priced at one‐third of the cost of glass fiber or less), weight reduction (these fibers are half the weight of glass fiber), recycling (natural fiber composites are easier to recycle) and the desire for green products. This Review provides an overview of natural fiber reinfocred composites focusing on natural fiber types and sources, processing methods, modification of fibers, matrices (petrochemical and renewable), and their mechanical performance. It also focuses on future research, recent developments and applications and concludes with key issues that need to be resolved. This article critically summarizes the essential findings of the mostly readily utilized reinforced natural fibers in polymeric composite materials and their performance from 2000 to 2013.     

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     

Inverse gas chromatography for the determination of the dispersive surface free energy and acid–base interactions of a sheet molding compound. I. Matrix material and glass

Sheet molding compound is a material composed of a polyester thermosetting matrix with a thermoplastic, an inorganic filler, a metal oxide, reinforcement fibers, and material performance enhancers embedded in the crosslinked matrix. To achieve the optimum mechanical properties required for the composite material, the surface free energy of the polyester composite needs to be understood. In this study, the composite matrix and glass reinforcement fibers are compared with respect to their surface free energy and acid–base characteristics on the basis of inverse gas chromatography measurements. The inverse gas chromatography results for the matrix and glass are compared to previous results found for sized and unsized cellulosic fibers. The inverse gas chromatography data are used to assess chemical modifications performed on the biobased fibers to predict improvements in the fiber/matrix interaction, and this provides inferences on the overall composite cohesion. Our results show first that any fiber reinforcement system for the polyester composite material has to be acidic to promote good adhesion as the matrix system is very basic and second that the individual dispersive surface energies of the components of the matrix interact in a weighted average to determine the overall surface energy of the composite. Also, a commercial glass reinforcement sized for polyester has been found to have a lower interaction parameter than literature values for cellulosic fibers. This finding suggests that cellulosic fibers might have an advantage in competing with a conventional glass‐fiber reinforcement system in fiber/matrix bonding for sheet molding compound composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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