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     

Biocomposites developed using water‐plasticized wheat gluten as matrix and jute fibers as reinforcement

Biocomposites developed from wheat gluten using water without any chemicals as plasticizer and jute fibers as reinforcement have much better flexural and tensile properties than similar polypropylene composites reinforced with jute fibers. Wheat gluten is an inexpensive and abundant co‐product derived from renewable resources and is biodegradable but non‐thermoplastic. Previous attempts at developing biocomposites from wheat gluten have used plasticizers such as glycerol or chemical modifications to make gluten thermoplastic. However, plasticizers have a considerably negative effect on the mechanical properties of the composites and chemical modifications make wheat gluten less biodegradable, expensive and/or environmentally unfriendly. In the research reported, we developed composites from wheat gluten using water as a plasticizer without any chemicals. Water plasticizes wheat gluten but evaporates during compression molding and therefore does not affect the mechanical properties of the composites. The effect of composite fabrication conditions on the flexural, tensile and acoustic properties was studied in comparison to polypropylene composites reinforced with jute fibers. Wheat gluten composites had flexural strength (20 MPa), tensile strength (69 MPa) and tensile modulus (7.7 GPa) values approximately twice those of polypropylene composites. Water is an effective plasticizer for wheat gluten and could be used to develop various types of inexpensive and biodegradable wheat gluten‐based thermoplastics. Copyright © 2011 Society of Chemical Industry     

Effect of Glutaraldehyde Crosslinking Conditions on the Strength and Water Stability of Wheat Gluten Fibers

Regenerated protein fibers from plant proteins including wheat gluten lack the mechanical properties and water stability desired for usual applications. Crosslinking has been used to improve the properties of regenerated proteins fibers. Although glutaraldehyde is commonly used to crosslink proteins, the effect of various crosslinking conditions on the properties of the materials has not been studied. In this work, a systematic study of glutaraldehyde crosslinking conditions of wheat gluten fibers is presented and shows that even low concentrations of glutaraldehyde (0.05%) can improve the strength and water stability of wheat gluten fibers.

     

The Effect of Silane Coupling Agents on the Viscoelastic Properties of Rubber Biocomposites

Summary: This paper deals with the dynamic mechanical study of sisal/oil palm hybrid fiber reinforced natural rubber composites (at frequency 1 Hz) with reference to the role of silane coupling agents. Composites were prepared using sisal and oil palm fibers subjected to chemical modifications with different types of silane coupling agents. The silanes used were Silane F8261 [1,1,2,2‐perfluorooctyl triethoxy silane], Silane A1100 [γ‐aminopropyltriethoxy silane] and Silane A151 [vinyl triethoxy silane]. It was observed that for treated composites, storage modulus and loss modulus increased while the damping property was found to decrease. Maximum E' was exhibited by the composite prepared from fibers treated with silane F8261 and minimum by composites containing fibers treated with silane A151. This was attributed to the reduced moisture absorbing capacity of chemically modified fibers leading to improved wetting. This in turn produced a strong interfacial interface giving rise to a much stiffer composite with higher modulus. Surface characterization of treated and untreated sisal fibers by XPS showed the presence of numerous elements on the surface of the fiber. Scanning electron micrographs of tensile fracture surfaces of treated and untreated composites demonstrated better fiber–matrix bonding for the treated composites.

Scheme of interaction of silanes with cellulosic fibers.     

A New Class of Injection Moulded Structural Biocomposites from PHBV Bioplastic and Carbon Fibre

Biocomposites from carbon fibre (CF) and poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) bioplastic were fabricated by extrusion followed by injection moulding. The effects of fibre length and fibre loading on the performance of PHBV/CF composites were investigated. The amount of CF (for both 150 µm and 6 mm length) was varied from 10 to 40 wt.‐%. The significant improvement in tensile strength (65%) and flexural strength (96%) was observed at 30 wt.‐% CF (6 mm length) loading. The heat deflection temperature (HDT) of the PHBV/CF composites increased by 32% compared to neat PHBV. The fibre–matrix interaction was analysed using scanning electron microscopy (SEM). The tensile modulus of the composites was evaluated theoretically by the rule of mixture and the Hirsch model.

     

Aspects of alkali treatment of sponge gourd (Luffa cylindrica) fibers on the flexural properties of polyester matrix composites

Sponge gourd (Luffa cylindrica) forms a natural mat that deviates the crack path in brittle thermoset resin matrix composites, leading to a controlled fracture mode and increasing the toughness of the composite. The use of luffa as reinforcement is, however, restricted by a very weak fiber–matrix interface. In this work, luffa fibers were alkali‐treated at two temperatures, with varying alkali concentrations. Although the surface analysis shows that the treatments promote a clear removal of the outer surface layer of the fibers with the exposition of the inner fibrillar structure and the consequent increase of the fiber surface area, only a secondary increase on the mechanical properties was obtained. The slight increase observed was attributed only to mechanical interlock. Long pullout lengths and neat fiber beads were the main features observed at the fracture surface of the treated and untreated fiber composites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1927–1932, 2003     

Mechanical and Water Absorption Properties of Natural Fibers/Polymer Biocomposites

In the present communication a study on the preparation and characterizations of Pine Needles (PN) reinforced polymers using Phenol-Formaldehyde (PF) as a novel polymer matrix has been reported. Pine Needles (PN) of different dimensions were used to prepare biocomposites. The influence of different fiber dimension on the mechanical properties of the composites was determined. Analysis of morphological (SEM) and thermal (TGA/DTA) properties of Pine Needles, PF resin and polymer composites have also been carried out. These polymer composites were further subjected to various standardized characterization tests such as swelling under different solvents, moisture absorption and chemical resistance analysis.     

Unmodified and Modified Surface Sisal Fibers as Reinforcement of Phenolic and Lignophenolic Matrices Composites: Thermal Analyses of Fibers and Composites

Summary: The study and development of polymeric composite materials, especially using lignocellulosic fibers, have received increasing attention. This is interesting from the environmental and economical viewpoints as lignocellulosic fibers are obtained from renewable resources. This work aims to contribute to reduce the dependency on materials from nonrenewable sources, by utilizing natural fibers (sisal) as reinforcing agents and lignin (a polyphenolic macromolecule obtained from lignocellulosic materials) to partially substitute phenol in a phenol‐formaldehyde resin. Besides, it was intended to evaluate how modifications applied on sisal fibers influence their properties and those of the composites reinforced with them, mainly thermal properties. Sisal fibers were modified by either (i) mercerization (NaOH 10%), (ii) esterification (succinic anhydride), or (iii) ionized air treatment (discharge current of 5 mA). Composites were made by mould compression, of various sisal fibers in combination with either phenol‐formaldehyde or lignin‐phenol‐formaldehyde resins. Sisal fibers and composites were characterized by thermogravimetry (TG) and DSC to establish their thermal stability. Scanning electron microscopy (SEM) was used to investigate the morphology of unmodified and modified surface sisal fibers as well as the fractured composites surface. Dynamic mechanical thermoanalysis (DMTA) was used to examine the influence of temperature on the composite mechanical properties. The results obtained for sisal fiber‐reinforced phenolic and lignophenolic composites showed that the use of lignin as a partial substitute of phenol in phenolic resins in applications different from the traditional ones, as for instance in other than adhesives is feasible.

Micrograph of the impact fracture surface of phenolic composite reinforced with mercerized sisal fiber (500 X).     

Biocomposites based on sea algae fibers and biodegradable thermoplastic matrices

Composites were prepared by mixing thermoplastic biodegradable polymers with sea algae fibers. Tensile mechanical properties were analyzed as a function of fiber concentration. The effect of processing, such as compression molding and calendering, on the mechanical properties of the materials was investigated. Composites showed higher elastic modulus and lower strength than the matrix components. Fiber damaging, characterized by a reduction of both length and diameter, was observed in the composites. Films, prepared by calendering operations, showed anisotropic properties due to fiber alignment. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 583–592, 1999     

Effects of Simple Abrasive Combing and Pretreatments on the Properties of Pineapple Leaf Fibers (Palf) and Palf-Vinyl Ester Composite Adhesion

Despite being mechanically and environmentally sound, pineapple leaf fibers (PALF) are of little use in Malaysia and the least studied for composite applications. In this study effects of abrasive combing and simple pretreatments on PALF and their adhesion to vinyl ester were investigated. In pineapple leaves, PALF are present in top lamina as large vascular bundles and bottom lamina as fine strands. Tensile strength and modulus of fine PALF strands are 155% and 134% higher than those of vascular bundles respectively. Abrasive combing reduced PALF diameters by 50.3% resulting in finer bundles with 48.6% higher modulus and 51.5% greater strength without much negative effects on fiber integrity. Water-soak did not change PALF tensile properties significantly, while dilute sodium hypochlorite (NaOCl) solution improved PALF modulus and strength by as much as 123% and 35% respectively while reducing elongation at break by 47%. Dilute solution of NaOCl changed PALF structurally through higher crystallinity and closer packing resulting in increased tensile strength and modulus. PALF thermal stability was also enhanced. PALF-vinyl ester adhesion improved due to bleach pretreatment indicated by significantly reduced fiber pull-out length of broken PALF-vinyl ester composites. Morphological study using scanning electron microscope was used to confirm the findings. This study indicated that abrasive combing and simple pretreatment of dilute sodium hypochlorite are potential techniques to produce cost-effective PALF for reinforcing plastics.     

The effects of clay dispersion on the mechanical,physical, and flame‐retarding properties of wood fiber/polyethylene/clay nanocomposites

In this study, nanosized clay particles were introduced into wood fiber/plastic composites (WPCs) to improve their mechanical properties and flame retardancy, which are especially important in various automotive and construction applications. A high degree of exfoliation for nanoclay in the wood fiber/high density polyethylene (HDPE) composites was successfully achieved with the aid of maleated HDPE (PE‐g‐MAn), through a melt blending masterbatch process. The structures and morphologies of the composites were determined using X‐ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. This article presents the effects of clay content and degree of clay dispersion on the mechanical and physical properties and flame retardancy of wood fiber/HDPE composites that contained a small amount of clay, in the range of 3–5 wt %. We concluded that achieving a higher degree of dispersion for the nanosized clay particles is critical to enhance the mechanical properties and the flame retardancy of WPCs when small amounts of clay are used. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Composites of Plasticized Polyamide 66 and Chemically Modified Vegetal Fibers

This work aims to prepare composites of polyamide 66 with vegetal fibers from curauá, jute, and flax. Alkaline treatment was conducted followed by silanization, improving the thermal properties of treated natural fibers. To reduce the processing temperature of polyamide 66, a combination of LiCl and N-butylbenzenesulfonamide was added to pure polyamide 66. It is shown that plasticizing polyamide 66 is one way to prepare composites with natural fibers using this high temperature polymer. The increase in elastic modulus of polyamide 66 and the decrease in strain at break were observed.     

Influence of fiber modification on interfacial adhesion and mechanical properties of pineapple leaf fiber‐epoxy composites

Three kinds of surface treatment, that is, the alkalization (5% w/v NaOH aqueous solution), the deposition of diglycidyl ether of bisphenol A (DGEBA) from toluene solution (1% w/v DGEBA), and the alkalization combined with the deposition of DGEBA (5% w/v NaOH/1% w/v DGEBA) were applied to modify interfacial bonding and to enhance mechanical properties of pineapple leaf fiber (PALF) reinforced epoxy composites. The fiber strength and strain were measured by single fiber test and the fiber strength variation was assessed using Weibull modulus. Furthermore, a fragmentation test was used to quantify the interfacial adhesion of PALF‐epoxy composite. It was verified that the interfacial shear strength of modified PALFs was substantially higher than that of untreated PALF by almost 2–2.7 times because of the greater interaction between the PALFs and epoxy resin matrix. The strongest interfacial adhesion was obtained from the fibers that had been received the alkalization combined with DGEBA deposition. Moreover, the flexural and impact properties of unidirectional PALF‐epoxy composites were greatly enhanced when reinforced with the modified PALFs due to an improvement in interfacial adhesion, particularly in the synergetic use of 5% NaOH and 5% NaOH/1% DGEBA. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of crosslinker and nanoclay on jute fabric reinforced soy flour green composite

Bio‐based composites were prepared by using soy flour, jute, glutaraldehyde (GA), nanoclay, and glycerol. An optimum concentration of glycerol was used as a plasticizer. The synthesized composites were characterized by various techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The exfoliation of clay layers was detected both by XRD and TEM study. FTIR study showed an interaction between clay, jute, and soy flour. The percentage content of GA and nanoclay was found to have profound influence on various physical properties of the composites. The increase in the concentration of GA and nanoclay improved the thermal stability, flame retardancy, dimensional stability, and most importantly the mechanical properties of the prepared composite. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mechanical Behavior and Fracture Toughness of Poly(L‐lactic acid)‐Natural Fiber Composites Modified with Hyperbranched Polymers

Summary: The use of hyperbranched polymers (HBP) with hydroxy functionality as modifiers for poly(L ‐lactic acid) (PLLA)‐flax fiber composites is presented. HBP concentrations were varied from 0 to 50% v/v and the static and dynamic tensile properties were investigated along with interlaminar fracture toughness. Upon addition of HBP, the tensile modulus and dynamic storage modulus (E′) both diminished, although a greater decline was noticed in the static modulus. The elongation of the composites with HBP showed a pronounced increase as large as 314% at 50% v/v HBP. The loss factor (tan δ) indicated a lowering of the glass transition temperature (T_g) due to a change in crystal morphology from large, mixed perfection spherulites to finer, smaller spherulites. The change in T_g could have also resulted from some of the HBP being miscible in the amorphous phase, which caused a plasticizing effect of the PLLA. The interlaminar fracture toughness measured as the critical strain energy release rate (G_IC) was significantly influenced by HBP. At 10% v/v HBP, G_IC was at least double that of the unmodified composite and a rise as great as 250% was achieved with 50% v/v. The main factor contributing to high fracture toughness in this study was better wetting of the fibers by the matrix when the HBP was present. With improved ductility of the matrix, it caused ductile tearing along the fiber‐matrix interface during crack propagation.

ESEM photograph of propagation region of the interlaminar fracture toughness specimens with 30% v/v of HBP.     

On the characterization and spinning of an organic‐purified lignin toward the manufacture of low‐cost carbon fiber

A Kraft hardwood lignin (HWL) and an organic‐purified hardwood lignin (HWL‐OP) were evaluated as potential precursors for the production of low‐cost carbon fibers. It was found that the unpurified HWL exhibited poor spinnability while the HWL‐OP exhibited excellent spinnability characteristics. Fibers of various diameters were obtained from the HWL‐OP. Thermostabilization studies showed that oxidative stabilization can only be used to convert HWL‐OP‐based fibers into carbon fibers if extremely low heating rates are applied. Carbonized lignin‐based fibers had tensile strength of 0.51 GPa and tensile modulus of 28.6 GPa. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

PE–HD/改性剑麻纤维复合材料的制备及性能

以高密度聚乙烯(PE–HD)为基体材料,剑麻纤维(SF)为增强填充材料,利用不同的偶联剂(硅烷偶联剂,钛酸酯偶联剂)改性SF,用熔融共混法制备一系列PE–HD/SF复合材料。采用扫描电子显微镜、广角X射线衍射仪、差示扫描量热仪、维卡软化仪及万能试验机等测试了复合材料的微观形貌、结晶性能、热及力学性能。结果表明,偶联剂改性的SF与PE–HD有着较好的界面结合,SF的添加使得PE–HD的结晶度下降,热变形温度提高;与未改性的SF相比,当硅烷偶联剂改性SF添加量为10%时,PE–HD基复合材料的拉伸强度、弯曲强度和冲击强度明显提高。     

Preparation and mechanical properties of high‐performance short ramie fiber‐reinforced polypropylene composites

Short ramie fiber (RF) was used to reinforce the polypropylene (PP). The composites were prepared in a twin‐screw extruder followed by injection molding. The experimental results showed that both the strength and the modulus of the composites increase considerably with increasing RF content. The tensile strength and flexural strength are as high as 67 and 80 MPa by the incorporation of ramie up to 30 wt %. To the best of our knowledge, this is one of the best results for short natural fiber‐reinforced PP composites. However, the preparation method in this study is more simple and economic. This short RF‐reinforced PP composites extend the application field for short‐nature fiber‐reinforced PP composites. Morphological analysis revealed that it is the high aspect ratio of the fiber and good interfacial compatibility that result in the high performance of the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011