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.     

The role of interface modification on the mechanical properties of injection-moulded composites from commingled polypropylene/banana granules

Commingled polypropylene (PP)/banana granules were fabricated from slivers by mixing PP fibers and banana fibers by textile equipment. By twisting the sliver, the reinforcing fibers were compacted and bonded with the molten matrix material. PP/banana composites were prepared from commingled PP/banana granules by injection moulding method with special reference to the effect of maleic anhydride modified polypropylene (MAH-PP) concentration. The mechanical properties of the composites were found to depend on the concentration of MAH-PP. The tensile and flexural properties of the composites increased with the addition of MAH-PP up to 2 wt%. After 2 wt% addition of MAH-PP, these properties tend to be stabilized. On the other hand the unmodified composites showed the maximum impact strength. Fourier transform infrared spectroscopic (FTIR) analysis of the MAH-PP modified composites showed evidence of a chemical bridge between the hydroxyl group of the banana fiber and maleic anhydride of the MAH-PP through an esterification reaction. The feature peak of the esterification occurred in the range ～ 1743 cm^?1. In order to confirm the esterfication reaction further, FTIR spectra of the banana microfibrils and MAH-PP modified PP/banana microfibril composites were taken and compared. The tensile fracture surfaces of the unmodified and MAH-PP modified PP/banana composites were studied by scanning electron microscopy (SEM). An improvement in adhesion between the fiber and the matrix was observed in the case of MAH-PP modified composites. Two different processing methods, both injection and compression mouldings were performed to prepare the PP/banana composites. Tensile properties of the composites prepared by these two methods were compared. The enhancement of tensile properties for injection-moulded composites compared to the compression-moulded composites is owing to the occurrence of orientation, better mixing and interaction between the fiber and the matrix during injection moulding. Finally, experimental results of the tensile properties of the injection-moulded composites have been compared with theoretical predictions.     

Water Desorption Kinetics of Polymer Composites with Cellulose Fibers as Filler

The water desorption kinetics of polymer composite systems with hydrophilic cellulose fibers from recycled paper (PSP) filler embedded in various polymer matrices (hydrophobic thermoset epoxy resin [EP] and thermoplastic polypropylene [PP], and hydrophilic thermoplastic poly[vinyl alcohol] [PVA]) was studied. Polymer composites test pieces containing 0, 3, 6, 9, and 30 wt. % of fibers were prepared. Adhesion between fibers and polymer matrices was improved by utilization of maleic anhydride grafted polypropylene (MAPP) coupling agent in the case of thermoplastic matrices (both PP and PVA). Water desorption tests were conducted after immersing test pieces in a distilled water bath at room temperature for 24 h. Study of the water desorption kinetics proved the expected enhanced absorption of the resulting composites after incorporation of cellulose fibers. A difference between two similar types of PVA by measurement of the desorption kinetics was found.     

Thermal behavior of chemically treated and untreated sisal fiber reinforced composites fabricated by resin transfer molding

Using thermogravimetric analysis (TGA), the thermal behavior of sisal fibers and sisal/polyester composites, fabricated by resin transfer molding (RTM), has been followed. Chemical treatments have been found to increase the thermal stability, which has been attributed to the resultant physical and chemical changes. Scanning electron microscopy (SEM) and infrared (FT-IR) studies were also performed to study the structural changes and morphology in the sisal fiber during the treatment. The kinetic studies of thermal degradation of untreated and treated sisal fibers have been performed using Broido method. In the composites, as the fiber content increases, the thermal stability of the matrix decreases. The treated fiber reinforced composites have been found to be thermally more stable than the untreated derivatives. The increased thermal stability and reduced moisture behavior of treated composites have been correlated with fiber/matrix adhesion.     

Composites from Brazilian natural fibers with polypropylene: mechanical and thermal properties

Brazil has a well established ethanol production program based on sugarcane. Sugarcane bagasse and straw are the main by-products that may be used as reinforcement in natural fiber composites. Current work evaluated the influence of fiber insertion within a polypropylene (PP) matrix by tensile, TGA and DSC measurements. Thus, the mechanical properties, weight loss, degradation, melting and crystallization temperatures, heat of melting and crystallization and percentage of crystallinity were attained. Fiber insertion in the matrix improved the tensile modulus and changed the thermal stability of composites (intermediary between neat fibers and PP). The incorporation of natural fibers in PP promoted also apparent T _c and ΔH _c increases. As a conclusion, the fibers added to polypropylene increased the nucleating ability, accelerating the crystallization process, improving the mechanical properties and consequently the fiber/matrix interaction.     

Effect of Fiber Surface Modification on the Interfacial and Mechanical Properties of Kenaf Fiber-Reinforced Thermoplastic and Thermosetting Polymer Composites

The surfaces of kenaf fibers were treated with three different silane coupling agents. 3-glycidoxypropyltrimethoxy silane (GPS), 3-aminopropyltriethoxy silane (APS), and 3-methacryloxypropyltrimethoxy silane (MPS). Among them, the most effective one for the property improvement was GPS when it was applied to the kenaf fiber surfaces at 0.5 wt%. Thermoplastic polypropylene (PP) and thermosetting unsaturated polyester (UPE) matrix composites with chopped kenaf fibers untreated and treated at different GPS concentrations from 0.1 wt% to 5 wt% were fabricated using compression molding technique. The present study demonstrates that the interfacial, flexural, tensile, and dynamic mechanical properties of both kenaf/PP and kenaf/UPE composites importantly depend on the GPS treatments done at different concentrations. The greatest property improvement of both thermoplastic and thermosetting polymer composites was obtained with the silane treatment at 0.5 wt% and the mechanical properties were comparable with E-glass composites prepared the same polymer matrix under the corresponding fiber length and fiber loading. The results also agreed with each other with regard to their interfacial shear strength, flexural properties, tensile properties, storage modulus, with support of fracture surfaces of the composites.     

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.     

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.     

Interfacial effects in short sisal fiber/maleated castor oil foam composites

In this study, bio-foam composites are produced using short sisal fiber as the reinforcement and modified castor oil as the matrix, respectively. The foam composites with an average cell size of 200 μm possess properties similar to those of commercial polyurethane foams. The effects of fiber loading, fiber length and foam density on the compressive properties of the foam composites are reported in relation to the interfacial interaction. It is found that the addition of chopped sisal alters cell structure of the foam. Surface pre-treatment of sisal by alkali or silane coupling agent helps to improve the mechanical properties and interfacial adhesion. The exposure of the fibers to the gas cells of the foam reduces the effectiveness of interfacial effect, which is different from the case of conventional bulk composites. As a result, the reinforcing ability of sisal fibers becomes a function of fiber length and so on.     

Modification of nano-kenaf surface with maleic anhydride grafted polypropylene upon improved mechanical properties of polypropylene composite

The surface of nano-kenaf fiber is modified with maleic anhydride grafted polypropylene (MA-g-PP) and added into PP and the mechanical properties and the flow property of the composite are investigated. The addition of MA-g-PP in nano-kenaf/PP composite increases the tensile strength, the elongation%, and the impact strength (I.S.), while it decreases the flow property (melt flow index) compared to without MA-g-PP composite (nano-kenaf/PP). The scanning electron microscope photograph shows it also increases interfacial adhesion between nano-kenaf and PP matrix. Regardless of MA-g-PP, nano-kenaf fibers shows better adhesion with PP compared to micron-kenaf fibers. Addition of MA-g-PP further improved interfacial adhesion between nano-kenaf surface and PP matrix compared to without MA-g-PP nano-kenaf compound. The addition of MA-g-PP apparently improves the interfacial adhesion between nano-kenaf surface and PP by formation of 3-dimensional network structure.     

Influence of chemical treatments on the interfacial adhesion between sisal fibre and different biodegradable polymers

The influence of chemical treatments on the interfacial adhesion of sisal fibres and biodegradable matrices were studied in the present work. For that purpose, four different polymers were used: polycaprolactone (PCL), cellulose acetate, MaterBi Z (a commercial starch/polycaprolactone blend) and MaterBi Y (a commercial starch/cellulose derivatives blend). Alkaline and acetylation treatments were performed on sisal fibres. Properties were determined by means of tensile tests, adhesion measurements and contact angle determination. The interfacial shear strength was correlated with the hydrophilic character of the material.     

Fabrication and Flexural Properties of Bagasse Fiber Reinforced Biodegradable Composites

Biodegradable composites made from bagasse fiber and biodegradable resin were fabricated and the flexural properties of the composites investigated in terms of the effects of fiber length, fiber volume fraction, and different alkali treatments of the bagasse fibers. The flexural properties of the composites increased with the increase in fiber length but decreased below the critical fiber length. The flexural properties increased with the increase in fiber volume fraction. The scanning electron microscope (SEM) micrographs showed that compression of the cellulose structure of bagasse fiber after preparation could have caused enhancement in the flexural properties. Furthermore, when comparing the effects of different alkali treatments of the bagasse fibers, maximum improvement in the flexural properties was observed for the 1% NaOH solution treated fiber composites. After alkali treatment, fibrillation occurred and the surface of the treated fibers became finer; this could contribute to improvement in the fiber‐matrix adhesion and result in enhancing the flexural properties.     

Banana fiber/chemically functionalized polypropylene composites with in-situ fiber/matrix interfacial adhesion by Palsule process

Chemically functionalized maleic anhydride (MAH)-grafted polypropylene matrix has been used (in place of polypropylene as matrix with compatibilizer) to process banana fiber/chemically functionalized polypropylene (BF/CFPP) composites, without using any compatibilizer and without any fiber modification by Palsule process. Fiber/matrix interfacial adhesion generated, in-situ, due to interactions between BF and the MAH of the CFPP matrix has been established by Fourier transform infrared spectroscopy and scanning electron microscopy. Mechanical properties of the BF/CFPP composites developed by Palsule process with in-situ fiber/matrix interfacial adhesion in this study have been found to be higher than those of the matrix and it increases with increasing amounts of fibers in composites, and are better than properties of literature reported BF/polypropylene composites processed with compatibilizers. Measured modulus of BF/CFPP composites compares well with values predicted by rule of mixtures, Hrisch model, Halpin-Tsai equations and its modified Nielsen version, and with Palsule equation. The feasibility of developing natural fiber/MAH grafted polyolefin composites by Palsule process without using any compatibilizer and without any fiber treatment is demonstrated.     

Discontinuous basalt and glass fiber reinforced PP composites from textile prefabricates: effects of interfacial modification on the mechanical performance

Spun and blown basalt fibers and their PP matrix composites were investigated. The composites were manufactured by hot pressing technology from carded and needle punched prefabricate using PP fiber as matrix material. Glass and blown basalt fibers were treated with reaction product of maleic acid-anhydride and sunflower oil while spun basalt fibers had a surface coating of silane coupling agent. Fibers were investigated with tensile tests while composites were subjected to static and dynamic mechanical tests. The results show that blown basalt fibers have relatively poor mechanical properties, while spun basalt fibers are comparable with glass fibers regarding geometry and mechanical performance. The static and dynamic mechanical properties of glass and spun basalt fiber reinforced composites are similar and are higher than blown basalt fiber reinforced composites. Results were supported with SEM micrographs.     

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.     

Effect of fiber surface treatments on the fiber–matrix interaction in banana fiber reinforced polyester composites

Cellulosic fibers have been used as cost-cutting fillers in plastic industry. Among the various factors, the final performance of the composite materials depends to a large extent on the adhesion between the polymer matrix and the reinforcement and therefore on the quality of the interface. To achieve optimum performance of the end product, sufficient interaction between the matrix resin and the cellulosic material is desired. This is often achieved by surface modification of the resin or the filler. Banana fiber, the cellulosic fibers obtained from the pseudo-stem of banana plant (Musa sepientum) is a bast fiber with relatively good mechanical properties. The fiber surface was modified chemically to bring about improved interfacial interaction between the fiber and the polyester matrix. Various silanes and alkali were used to modify the fiber surface. Modified surfaces were characterized by SEM and FTIR. The polarity parameters of the chemically modified fibers were investigated using the solvatochromic technique. The results were further confirmed by electrokinetic measurements. Chemical modification was found to have a profound effect on the fiber–matrix interactions. The improved fiber–matrix interaction is evident from the enhanced tensile and flexural properties. The lower impact properties of the treated composites compared to the untreated composites further point to the improved fiber–matrix adhesion. In order to know more about the fiber–matrix adhesion, fractured surfaces of the failed composites where further investigated by SEM. Of the various chemical treatments, simple alkali treatment with NaOH of 1% concentration was found to be the most effective. The fiber–matrix interactions were found to be dependent on the polarity of the modified fiber surface.     

Sodium Borohydride as a Protective Agent for the Alkaline Treatment of Sisal Fibers for Polymer Composites

The vegetable fibers used for polymer matrix composites are usually treated to improve their adhesion with the matrix. The chemical treatment with sodium hydroxide (NaOH), although widely used, may damage the fiber surface structure, reducing its strength. The possibility of protecting vegetable fibers against alkaline chemical aggression by using hydride ions (H^–) was investigated in this work. Sisal fibers were modified by immersion in a NaOH aqueous solution (2, 5 and 10% wt/vol), with or without the addition of sodium borohydride (NaBH₄) (1% wt/vol), under variable conditions (immersion time and temperature). The effect of using NaBH₄ was investigated using fiber tensile and pull-out tests, critical length calculation, along with a Weibull statistical analysis. This agent was found to minimize sisal degradation under highly concentrated alkaline conditions in comparison with sisal treated with the pure NaOH solution. The results suggest the 5% wt/vol treatment for 60 min under room temperature in the presence of the hydride ions as the most suitable for sisal. This result may be extended to other vegetable fibers of similar composition and may promote their use in polymer composites.     

Structure and Properties of Glass Fiber Reinforced Polypropylene/Liquid Crystal Polymer Blends

A liquid crystal polymer (LCP) was used to improve the physical properties of glass fiber reinforced polypropylene (GFRPP). The LCP was beneficial to improve the mechanical and heat resistant properties of the GFRPP/LCP composite. Compared with the GFRPP with 30% (w%) glass fiber (GF), the yield strength and the impact strength for the GFRPP/LCP composites increased by 62.7% and 18.1%, respectively, with a 6.8°C increase in the Vicat softening temperature for a 5% LCP addition to the GFRPP composites. The crystallinity of the polypropylene (PP) matrix for the GFRPP/LCP composites increased for 5% LCP and then decreased with increasing the LCP content. The γ-phase crystals for the PP matrix occurred in the shear layer of the injection molded GFRPP/LCP samples. The improved adhesion interface between the GF and the PP matrix was beneficial to reinforce and toughen the GFRPP/LCP composites with a small addition of the LCP.     

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.     

The Effects of Morphological Properties of Henequen Fiber Irradiated by EB on the Mechanical and Thermal Properties of Henequen Fiber/PP Composites

The aim of this study was to investigate the effects of electron beam (EB) irradiation on the morphological properties, crystallinity and surface area of henequen fiber and on the mechanical and thermal properties of henequen fiber reinforced polypropylene (PP) composites. The structure of henequen fiber was characterized by X-ray diffraction, mercury porosimetry and BET surface area analysis. The EB irradiation of 10 kGy led to the increasing of crystalline and surface pore area of henequen fiber, which contributed to the number of interlocking places with PP. From the results of tensile and impact strength tests, the highest value was observed for the composite reinforced with the henequen fiber treated with EB dose of 10 kGy, decreasing overall as EB dose increased. This tendency was also shown by coefficient of thermal expansion (CTE) measurements, but the value of CTE decreased until 50 kGy, meaning that a large total surface area can provide many interlocking places and so improve adhesion between fiber and matrix. Therefore, it can be concluded that the optimum pore surface area by 10 kGy irradiation contributes to successful mechanical interlocking between fiber and matrix and consequently enhances the mechanical and thermal properties of the composites.