Mechanical Properties Comparison of Various Ratios of L-Lactide Grafted Sisal Fibers and Untreated Sisal Fibers Reinforced Poly (lactic acid) Composites

Composites composed of the mixed fibers of L-lactide (LA) grafted sisal fiber (SF-g-LA) and untreated sisal fiber (USF) in a poly (lactic acid) (PLA) matrix were prepared with SF-g-LA/USF fibers ratios of 0, 1:9, 3:7, 5:5, 7:3, 9:1, and 1. The mechanical properties and the interfacial performance of the mixed SF reinforced PLA composites were investigated. The results of the study showed that the introduction of SF-g-LA improved the tensile strength, tensile modulus, flexural strength and flexural modulus of the mixed SF reinforced PLA composites compared with pure PLA or PLA composites with only USF, resulting from the improved interfacial adhesion between SF-g-LA and the PLA matrix. In addition, the introduction of some amount of USF enhanced the reinforcing efficiency of the mixed SF in the composites compared to the PLA composites with only SF-g-LA, owing to the good mechanical properties of USF itself. Furthermore, as for the tensile strength and tensile modulus of the mixed SF reinforced PLA composites, the optimal ratio of SF-g-LA and USF was 7:3, whereas for the flexural modulus of the mixed SF reinforced PLA composites, the optimal mixed ratio of SF-g-LA and USF was 3:7.     

Kenaf/polypropylene biocomposites: effects of electron beam irradiation and alkali treatment on kenaf natural fibers

Thermal and dynamic mechanical properties of kenaf natural fiber reinforced polypropylene (PP) biocomposites were examined to compare the effects of natural fiber treatment by electron beam irradiation (EBI) and alkalization. The alpha cellulose contents, the functional groups on the surfaces and the thermal stability of the untreated and treated kenaf fibers were studied. Kenaf fiber/polypropylene(PP) biocomposites were fabricated by means of a compression molding technique using chopped kenaf fibers treated with electron beam (EB) dosages of 100, 200, 500 kGy or with NaOH concentrations of 2, 5, 10 wt%, respectively. The thermal stability, the dynamic mechanical and the interfacial properties of untreated and treated kenaf/PP biocomposites were also investigated through a thermogravimetric analysis, a dynamic mechanical analysis and a fractographic observation, respectively. The results show that the characteristics of kenaf fibers and biocomposites depended on the different treatment level with the EB dosages or on the NaOH concentrations used. In this study, the modification of kenaf fiber surfaces at 200 kGy EBI and treatment with 5 wt% NaOH was most effective for improving the performance of kenaf/PP biocomposites. This study suggests that EBI can be used for modification of natural fiber as an environmentally friendly process and contribute to an improvement in the performances of kenaf/PP biocomposites.     

Effect of chemical modifications of the pineapple leaf fiber surfaces on the interfacial and mechanical properties of laminated biocomposites

Natural fiber reinforced renewable resource based laminated composites were prepared from biodegradable poly(lactic acid) (PLA) and untreated or surface-treated pineapple leaf fibers (PALF) by compression molding using the film stacking method. The objective of this study was to determine the effects of surface treatment of PALF on the performance of the fiber-reinforced composites. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were used to aid in the analysis. The mechanical properties of the PLA laminated composites were improved significantly after chemical treatment. It was found that both silane- and alkali-treated fiber reinforced composites offered superior mechanical properties compared to untreated fiber reinforced composites. The effects of temperature on the viscoelastic properties of composites were studied by dynamic mechanical analysis (DMA). From the DMA results, incorporation of the PALF fibers resulted in a considerable increase of the storage modulus (stiffness) values. The heat defection temperature (HDT) of the PALF fiber reinforced PLA laminated composites was significantly higher than the HDT of the neat PLA resin. The differential scanning calorimeter (DSC) results suggest that surface treatment of PALF affects the crystallization properties of the PLA matrix. Additionally, scanning electron microscopy (SEM) was used to investigate the distribution of PLA within the fiber network. SEM photographs of fiber surface and fracture surfaces of composites clearly indicated the extent of fiber–matrix interface adhesion. It was found that the interfacial properties between the reinforcing PALF fibers and the surrounding matrix of the laminated composite are very important to the performance of the composite materials and PALF fibers are good candidates for the reinforcement fiber of high performance laminated biodegradable biocomposites.     

Assessment of dicumyl peroxide ability to improve adhesion between polylactide and flax or hemp fibres

Dicumyl peroxide (DCP) is commonly applied as a cross-linking agent in polymer processing. The main aim of this work was to assess the ability of DCP to improve adhesion between polylactide (PLA) and flax or hemp fibres by their interphase cross-linking. Short fibre-reinforced PLA composites were manufactured due to the importance of short fibres in injection moulding of high-quality biocomposites. Reactive extrusion of the PLA, flax or hemp fibres, and DCP was performed. The flax or hemp fibre content was 10?wt%, while DCP varied with 0.5 and 2.5?wt%. The fibres and PLA were mechanically mixed, extruded, granulated and injection moulded to form samples for testing. The samples were characterized by differential scanning calorimetry (DSC), tensile and impact strength tests, dynamic mechanical analysis and scanning electron microscopy (SEM). It was found that flax and hemp fibres increased the Young’s modulus while these fibres decreased the impact strength. Addition of DCP led to increase in PLA crystallinity at the interface with fibres which led to further decrease in impact strength. For that reason, it was concluded that DCP is an ineffective agent to improve interphase adhesion between PLA and short flax or hemp fibres.     

Novel Jute/Polycardanol Biocomposites: Effect of Fiber Surface Treatment on Their Properties

In the present study, novel biocomposites with chopped jute fibers and thermosetting polycardanol were prepared using compression molding technique for the first time. Prior to biocomposite fabrication, jute fiber bundles were surface-treated at various concentrations using 3-glycidoxypropyltrimethoxy silane (GPS) and 3-aminopropyltriethoxy silane (APS), respectively. The interfacial shear strength, flexural properties and thermal properties of jute/polycardanol biocomposites reinforced with untreated and silane-treated jute fibers were investigated by means of single fiber microbonding test, three-point flexural test, dynamic mechanical analysis, thermogravimetric analysis and thermomechanical analysis. Both GPS and APS treatments played a role in improving the interfacial adhesion, reflecting that the organofunctional groups located at the end of silane coupling agents may contribute to linking between jute fibers and a polycardanol resin. As a result, it gave rise to increased interfacial shear strength of the biocomposites. Such interfacial improvement also led to increasing the flexural strength and modulus, storage modulus, thermal stability and thermomechanical stability.     

Lignocellulosic composites with grafted polystyrene interfaces

The effects of surface grafting of a polymer onto lignocellulosic fiber surface and processing methods on both the interfacial interactions and the resulting composite properties of the fiber-reinforced thermoplastic composites were investigated. Chemithermomechanical pulp (CTMP) wood fiber was used as a reinforcement, which has been chemically modified by radical polymer grafting of styrene onto the fiber surfaces. The chemically modified CTMP fiber was then compounded with polystyrene (PS). Two different processing methods, both compression and injection moldings, were performed to prepare the wood-fiber-reinforced composites. Experimental results showed that surface modification of wood fiber leads to an obvious increase in mechanical properties of the fiber-reinforced composites as compared to the untreated fiber composites. The enhancement of mechanical properties is much greater through injection molding compared with compression molding owing to occurrence of orientation, and better mixing and interaction between the fiber and the matrix by injection molding. An improvement in fiber wetting properties and adhesion by the matrix was observed through scanning electron microscopy for the surface grafted fiber reinforced composites. Untreated wood fiber exhibited a smooth surface without adhered polymer, indicating poor adhesion, while polymer attached to the surface was seen on treated cellulose fiber due to the higher fiber-matrix interactions.     

Improved interactions in chemically modified pineapple leaf fiber reinforced polyethylene composites

Mechanical properties of pineapple leaf fiber reinforced low density polyethylene composites have been studied with special reference to the effects of interface modifications. Various chemical treatments using reagents such as NaOH, PMPPIC, silane and peroxide were carried out to improve the interfacial bonding. Both infrared spectroscopy and SEM were used to characterize the interface and the modified fiber surface. It has been found that the treatments improved the mechanical properties significantly. However, the effect varied according to the nature of the treatments. SEM studies on the fracture surfaces revealed the extent of fiber-matrix adhesion. It has been observed that the PMPPIC treatment reduced the hydrophilicity of the fiber and thereby enhanced the mechanical properties of the composites. The addition of a small quantity of peroxide and silane increased the mechanical properties considerably. The action of peroxide is associated with the peroxide-induced grafting of polyethylene on the fiber surface. Among the various treatments, PMPPIC treatment of fiber exhibits maximum interfacial interactions. Attempts have been made to illustrate the interfacial bonding with the help of schematic models.     

Henequen/poly(butylene succinate) biocomposites: electron beam irradiation effects on henequen fiber and the interfacial properties of biocomposites

Henequen natural fiber-reinforced poly(butylene succinate) biocomposites were prepared through a resin microdroplet formation on a single fiber and also fabricated by a compression molding technique using chopped henequen fibers, surface-treated with electron beam irradiation (EBI) at various dosages. The effect of EBI treatment on the surface characteristics and dynamic mechanical properties of henequen fibers was investigated using SEM, XPS and DMA methods, respectively. Also, the interfacial behavior of biocomposites was explored through a single fiber microbonding test and fracture surface observations. The result indicates that the interfacial shear strength (IFSS) of biocomposites greatly depends on the EBI treatment level on the henequen fiber surface. This study also suggests that appropriate modification of natural fiber surfaces at an optimum EBI dosage significantly contributes to improving the interfacial properties of biocomposites.     

Microcellular and Solid Polylactide–Flax Fiber Composites

Polylactide–flax fiber composites with 1, 10 and 20 wt% fiber were melt-compounded and subsequently molded via the conventional and microcellular injection-molding processes. Silane was used as a coupling agent. The effects of fiber and silane content on cell morphology, static and dynamic mechanical properties, and crystallization properties have been studied. The average cell size decreased while the cell density increased with the fiber content. The degree of crystallinity increased with the fiber content. Silane treatment of fibers affected neither the cell morphology nor the degree of crystallinity. The toughness and strain-at-break of solid samples decreased with the fiber content while silane treatment increased both properties; however, neither fiber content nor silane treatment had much influence on the toughness and strain-at-break of microcellular samples. The specific modulus of both solid and microcellular samples increased with the fiber content. The specific strength of the solid and microcellular PLA–flax composites were only slightly lower than that of their solid and microcellular pure PLA counterparts. Overall, the toughness, strain-at-break, and specific strength of microcellular samples were found to be lower than that of their solid counterparts. The storage modulus of the PLA–flax composites with 10 and 20% fiber contents was higher than that of pure PLA.     

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

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

Surface treatment of single sisal fibers with bacterial cellulose and its enhancement in fiber-polymer adhesion properties

In this work, a simple and effective method to modify the surface of single sisal fibers with G. xylinum was described. Single fiber tensile strength test, single fiber fragmentation test, thermal gravimetric analyses were conducted to assess the effects of different modification methods (unmodified, NaOH treatment and BC treatment). Fourier transform infrared spectroscopy, scanning electron microscopy and water uptake experiments were employed to characterize the resulting interfacial adhesion. It was shown that BC treatment produced better reinforced polymer composites with improved mechanical and long-term properties. The results also elucidated that BC nanofibrils formed a dense three dimensional network on single sisal fibers covering the roughened surface and filling the grooves and other surface ‘defects’ caused by NaOH modification in addition to its exposed hydroxyl groups to form hydrogen bonds with sisal fiber, all contributed to enhanced mechanical properties of sisal fibers as well as the better binding between sisal fibers and resin matrix. Moreover, this work also confirmed that internal geometrical and morphological differences exist in sisal fibers and this result is insightful for future natural fiber research about the importance of careful selection of fibers for consistent comparisons.     

Effect of MAPP and TMPTA as compatibilizer on the mechanical properties of cellulose and oil palm fiber empty fruit bunch–polypropylene biocomposites

The effect of compatibilizers, namely, maleic anhydride grafted polypropylene (MAPP GR-205) and trimethylolpropane triacrylate (TMPTA), on the mechanical and morphological properties of the PP-cellulose (derived from oil palm empty fruit bunch fiber) and PP-oil palm empty fruit bunch fiber (EFBF) biocomposites has been studied. The ratio of PP : cellulose and PP : EFBF is fixed to 70 : 30 (wt/wt%) while the concentration of the compatibilizer is varied from 2.0 to 7.0 wt%. Results reveal that at 2.0 wt% of MAPP concentration, tensile strength of PP-EFBF biocomposite is significantly improved. This is due to the enhanced EFBF matrix adhesion resulting in an improvement in EFBF biocomposite performance. There are no significant changes observed in the PP-cellulose biocomposite properties upon the addition of MAPP. In contrast to the tensile strength, flexural modulus and impact strength are significantly improved with the addition of 2.0 wt% TMPTA to PP-cellulose biocomposite. The enhancement of mechanical properties in the presence of TMPTA is believed to be attributed to crosslinking of multifunctional monomer with the hydroxyl groups of cellulose.     

Improved mechanical properties of carbon fiber reinforced PTFE composites by growing graphene oxide on carbon fiber surface

The mechanical properties of carbon fiber reinforced polymer composites depend upon fiber-matrix interfacial properties. To improve the mechanical properties of ?bers/PTFE composites without sacri?cing tensile strength of ?bers, graphene oxide (GO) was introduced onto the surface of CFs by chemical vapour deposition (CVD). This hybrid coating increased the wettability and surface roughness of carbon fibers, which led to improved affinity between the carbon fibers and PTFE matrix. The resulting hybrid-coated carbon fiber-reinforced composites showed an enhancement in the short beam strength compared to un-coated carbon fiber composites. Meanwhile, a signi?cant increase of interlaminar shear strength (ILSS), interface shear strength tests (IFSS) and impact property were achieved in the 5-min-modi?ed CFs.     

Effect of Processing Parameters on the Interlaminar Shear Strength of Carbon Fiber/Epoxy Composites

The objective of this work was to improve the interlaminar shear strength of carbon fiber/epoxy composites by determining the effect on it of the processing parameters of the cured composites system, i.e., temperature, content of curing agent, and heating rate. Taguchi methodology and analysis of variance were applied for optimizing and statistically determining the significant factors that influenced the mechanical properties of the composites. It was found that the temperature and content of curing agent were equally the primary significant factors in controlling the interlaminar shear strength of the composites. Also, the correlation between water absorption and mechanical properties of the composites was investigated.     

Ballistic behavior of Heracron®-based composites: effect of fiber density and fabrication method

In this study, a Heracron^® aramid fiber-based helmet was made, and its ballistic properties were investigated. The effect of fiber density was studied in depth. For the same weight and number of plies, a helmet manufactured from the HT-2820-based composite showed improved ballistic properties compared with one made from the HT-15000-based composite. This result suggested that fiber density may strongly affect the ballistic properties of armor. HT-2820, containing more multifilament fibers, provides more efficient energy absorption and dissipation. The influence of fabrication method on the ballistic behavior of a helmet was studied. The V₅₀ of a helmet made by the film laminating method was 10% better than that for a helmet made by the resin dipping approach. Based on these findings, the film laminating method, which forms the composite by directly attaching aramid fabric to the matrix film, may be a good candidate for improving the ballistic behavior. The required composite interfacial strength will be application-dependent. Greater fiber-matrix adhesion may be advantageous in certain cases.     

Cellulose-based biocomposites: comparison of different multiphasic systems

Biocomposites (biodegradable composites) are obtained by blending biodegradable polymers and fillers. Since the main components are biodegradable, the composite as a whole is also expected to be biodegradable. This paper presents various biocomposites that have been elaborated with cellulose or lignocellulose fibers from diverse sources, with different lignin contents. This paper is targeted on the analysis of 'fiber–matrix' interactions of two types of biocomposites based on agropolymer (plasticized wheat starch) and biopolyester (polybutylene adipate-co-terephthalate), named APB and BPB, respectively. Processing and main properties of both biocomposites are shown and compared. Polyolefin-based composite (PPC), which is known to present very poor 'fiber–matrix' interactions, is used as a reference. Through the Young's modulus, mechanical properties have shown that the reinforcement, by increasing fiber content, is much more significant for APB compared to BPB. The evolution of chains mobility, evidenced through shift of T _g values, according to the increase in fiber content and thence in interfacial area, have shown that the fiber–matrix interactions are higher for APB. BPB presents intermediate values, higher than PPC ones. These results are in agreement with the analysis of the composite morphologies performed by SEM on cryogenic fractures. Finally, by determining the theoretical works of adhesion and the interfacial tensions from contact angle measurements, it is shown that these parameters are partially able to predict the level of interaction between the fibers and the matrix. We could show that the perspectives of such work seem to be of importance to tailor new materials with a controlled end-use.     

A comparative study of different nanoclay-reinforced cellulose nanofibril biocomposites with enhanced thermal and mechanical properties

The objective of this research was to comprehensively compare the effects of nanoclay bentonite (BT), halloysite nanotubes (HNTs) and sulfuric acid-etched halloysite nanotubes on the surface wettability, morphological, mechanical and thermal properties of cellulose nanofibril (CNF) biocomposites. A simple and environmental safe casting-evaporation method was used to fabricate these samples, which comprised up to 10 wt% of nanoclay. The surface wettability, tensile testing and TG results showed that the biocomposites with BT exhibited greater hydrophobicity, larger modulus and strength and better thermal stability than with HNTs at low content. However, at high content, the biocomposites with HNTs exhibited larger elongation at break. The DMA results indicated that biocomposites with HNTs exhibited better molecular motion restriction than with BT. These results combined with Fourier Transform Infrared (FTIR) also indicated interfacial interactions between CNF matrix and nanoclay. Acid treatment would help promote the interfacial interactions between HNTs and CNFs, resulting in enhanced mechanical and thermal properties. This comparative study will help in the choice of appropriate nanoclay for use in functional biomaterials in industrial production applications.     

Fiber-matrix adhesion mechanism of pitch-based carbon fiber composites

The fiber-matrix adhesion mechanism in high modulus pitch-based carbon fiber-epoxy matrix composites has been studied. The surface morphology and chemistry of the carbon fibers were examined by microscopic (SEM, STM), thermodynamic and spectroscopic (XPS, Raman) techniques. The interlaminar shear strength and transverse tensile strength of the composites made from surface-treated and untreated fibers were also obtained. In the microscopic analysis, there was no difference in the surface roughness between the surface-treated and untreated fibers. In the thermodynamic and spectroscopic analyses, surface treatment of the carbon fibers increased the amount of surface oxygen. The results indicated that the major role of the surface treatment on the carbon fiber-epoxy resin adhesion is not the mechanical interlocking effect by the surface roughness. The formation of surface oxygen-containing functional groups is assumed to account for the increase in fiber-matrix interfacial adhesion.     

Enhanced surface free energy of polyimide fibers by alkali treatment and its interfacial adhesion behavior to epoxy resins

In this article, polyimide (PI) fibers were modified by alkali treatment, and PI fiber-reinforced epoxy composites were fabricated. The effects of different alkali treatment times on the surface properties of the PI fibers and the adhesion behaviors of PI fiber/epoxy composites were studied. The surface morphologies, chemical compositions, mechanical properties, and surface free energy of the PI fibers were characterized by atomic force microscopy, X-ray photoelectron spectroscopy, single-fiber tensile strength analysis, and dynamic contact angle analysis, respectively. The results show that alkali treatment plays an important role in the improvement of the surface free energy and the wettability of PI fibers. We also found that, after the 3 min, 30 °C, 20 wt% NaOH solution treatment, the fibers possessed good mechanical properties and surface activities, and the interlaminar shear strength of the composites increased to 64.52 MPa, indicating good interfacial adhesion properties.     

Effects of plasma surface modification on the mechanical properties of carbon fiber and carbon fiber/epoxy composite

_The effect of surface treatment on mechanical properties of carbon fibers has been investigated by application of plasma polymerization of selected monomers in the vapor phase. The role of the fiber-matrix interface on carbon fiber-reinforced epoxy resin composites has also been studied. Composites have been prepared separately by the use of plasma-modified and unmodified carbon fibers in the epoxy resin matrix. The mechanical properties of carbon fibers (Hercules and Grafil) as well as of fiber/epoxy composites were examined by using single filament and three-point bending tests, respectively. It was observed that plasma polymerization treatment at selected plasma conditions led to significant improvement of interlaminar shear and flexural strength values of composites.