Wood‐fiber‐reinforced poly(lactic acid) composites: Evaluation of the physicomechanical and morphological properties

This article presents the results of a study of the processing and physicomechanical properties of environmentally friendly wood‐fiber‐reinforced poly(lactic acid) composites that were produced with a microcompounding molding system. Wood‐fiber‐reinforced polypropylene composites were also processed under similar conditions and were compared to wood‐fiber‐reinforced poly(lactic acid) composites. The mechanical, thermomechanical, and morphological properties of these composites were studied. In terms of the mechanical properties, the wood‐fiber‐reinforced poly(lactic acid) composites were comparable to conventional polypropylene‐based thermoplastic composites. The mechanical properties of the wood‐fiber‐reinforced poly(lactic acid) composites were significantly higher than those of the virgin resin. The flexural modulus (8.9 GPa) of the wood‐fiber‐reinforced poly(lactic acid) composite (30 wt % fiber) was comparable to that of traditional (i.e., wood‐fiber‐reinforced polypropylene) composites (3.4 GPa). The incorporation of the wood fibers into poly(lactic acid) resulted in a considerable increase in the storage modulus (stiffness) of the resin. The addition of the maleated polypropylene coupling agent improved the mechanical properties of the composites. Microstructure studies using scanning electron microscopy indicated significant interfacial bonding between the matrix and the wood fibers. The specific performance evidenced by the wood‐fiber‐reinforced poly(lactic acid) composites may hint at potential applications in, for example, the automotive and packaging industries. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4856–4869, 2006     

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     

Hemp‐fiber‐reinforced unsaturated polyester composites: Optimization of processing and improvement of interfacial adhesion

The processing variables for making hemp‐fiber‐reinforced unsaturated polyester (UPE) composites were optimized through orthogonal experiments. It was found that the usage of initiator, methyl ethyl ketone peroxide, had the most significant effect on the tensile strength of the composites. The treatment of hemp fibers with a combination of 1,6‐diisocyanatohexane (DIH) and 2‐hydroxyethyl acrylate (HEA) significantly increased tensile strength, flexural modulus of rupture, and flexural modulus of elasticity, and water resistance of the resulting hemp‐UPE composites. FTIR spectra revealed that DIH and HEA were covalently bonded to hemp fibers. Scanning electron microscopy graphs of the fractured hemp‐UPE composites demonstrated that treatment of hemp fibers with a combination of DIH and HEA greatly improved the interfacial adhesion between hemp fibers and UPE. The mechanism of improving the interfacial adhesion is proposed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of fiber modification with a novel compatibilizer on the mechanical properties and water absorption of hemp‐fiber‐reinforced unsaturated polyester composites

Hemp‐fiber‐reinforced unsaturated polyester (UPE) composites were prepared by compression molding. The treatment of hemp fibers with N‐methylol acrylamide (NMA) and sulfuric acid as a catalyst significantly increased tensile strength, flexural modulus of rupture and flexural modulus of elasticity, and water resistance of the resulting hemp–UPE composites. Fourier transform infrared (FTIR) spectra revealed that some NMA was covalently bonded to hemp fibers. Scanning electronic microscopy graphs of the fractured hemp–UPE composites revealed that treatment of hemp fibers with NMA greatly improved the interfacial adhesion between hemp fibers and UPE. The chemical reactions between hemp fibers and NMA as well as the mechanism of improving the interfacial adhesion were proposed and discussed. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

High Density Biocomposite from Natural Fibers and Tannin Resin

Abstract

Successful experiments on high, medium and low density natural fiber reinforced composites made from tannin/hexamine resin and flax–hemp fibers have recently been carried out. This study focused on the high density composites. In this work composite panels have been made of three different tannin extracts: mimosa, sulfited mimosa and quebracho, each with their own properties. The panels were tested for modulus in elasticity (MOE) in bending, and for swelling in cold water, following the French standard NF EN 622-2. It appeared that a strong correlation exists between the density and the mechanical performances of the composites. Water, which is necessary for hardening resin, can, when in excess cause a strong drop in the mechanical performances by increasing the porosity in a composite structure. In the course of carrying out this work, some manufacturing problems were found: cracks appeared during the pressing of large panels resulting in the need for a specific pressing cycle; and deformations occurred during the cooling phase due to internal stresses. Experimental procedures were developed and tested to reduce these problems.     

Investigating the acoustical properties of carbon fiber‐, glass fiber‐, and hemp fiber‐reinforced polyester composites

Wood is one of the main materials used for making musical instruments due to its outstanding acoustical properties. Despite such unique properties, its inferior mechanical properties, moisture sensitivity, and time‐ and cost‐consuming procedure for making instruments in comparison with other materials (e.g., composites) are always considered as its disadvantages in making musical instruments. In this study, the acoustic parameters of three different polyester composites separately reinforced by carbon fiber, glass fiber, and hemp fiber are investigated and are also compared with those obtained for three different types of wood specimens called poplar, walnut, and beech wood, which have been extensively used in making Iranian traditional musical instruments. The acoustical properties such as acoustic coefficient, sound quality factor, and acoustic conversion factor were examined using some non‐destructive tests based on longitudinal and flexural free vibration and also forced vibration methods. Furthermore, the water absorption of these polymeric composites was compared with that of the wood samples. The results reveal that the glass fiber‐reinforced composites could be used as a suitable alternative for some types of wood in musical applications while the carbon fiber‐reinforced composites are high performance materials to be substituted with wood in making musical instruments showing exceptional acoustical properties. POLYM. COMPOS., 35:2103–2111, 2014. © 2014 Society of Plastics Engineers     

Effects of alkalization on tensile,impact, and fatigue properties of hemp fiber composites

The effects of alkalization surface treatment on hemp fiber properties and the properties of hemp fiber–reinforced polyester composites have been studied. Hemp fibers were exposed to 1, 5, and 10% sodium hydroxide (NaOH) solutions. The tensile properties and interfacial shear strength of all alkalized fibers were found to lie within the range of nonalkalized fibers. Laminates were made of alkalized fibers with unsaturated polyester resin, using hand lay‐up and compression moulding. Alkalization of fibers at low concentrations of 1 and 5% resulted in improvements in tensile and fatigue properties of composites made from these fibers, but no such improvements were observed for 10% alkalized fiber composites. The improvements were attributed to improvement in fiber/matrix bonding after this treatment, which was also confirmed by scanning electron microscopy images. No improvement in impact damage tolerance was observed for any of these three alkalized fiber composites. Immersion in distilled water reduced water absorption compared with nonalkalized fiber composites; however, the tensile properties in water were similar to those for nonalkalized fiber composites. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Tribological behavior of short‐fiber‐reinforced polyimide composites under dry‐sliding and water‐lubricated conditions

Polyimide composites reinforced with short‐cut fibers such as carbon, glass, and quartz fibers were fabricated by the polymerization of monomer reactants process. The mechanical properties of the composites with different fiber contents were evaluated. The friction and wear properties of the polyimide and its composites were investigated under dry‐sliding and water‐lubricated conditions. The results indicated that the short‐carbon‐fiber‐reinforced polyimide composites had better tensile and flexural strengths and improved tribological properties in comparison with glass‐fiber‐ and quartz‐fiber‐reinforced polyimide composites. The incorporation of short carbon fibers into the polyimide contributed to decreases in the friction coefficient and wear rate under both dry and water‐lubricated conditions and especially under water lubrication because of the boundary lubrication effect of water. The polyimide and its composites were characterized by plastic deformation, microcracking, and spalling under both dry and water‐lubricated conditions, which were significantly abated under the water‐lubricated condition. The glass and quartz fibers were easily abraded and broken; the broken fibers transferred to the mating metal surface and increased the surface roughness of mating stainless steel, which led to the wear rate increasing for the glass‐fiber‐ and quartz‐fiber‐reinforced polyimide composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

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.     

Esterification effect of maleic anhydride on swelling properties of natural fiber/high density polyethylene composites

The natural fibers (banana, hemp, and sisal) and high density polyethylene were taken for the preparation of natural fiber/polymer composites in different ratios of 40 : 60 and 45 : 55 (w/w). These fibers were esterified with maleic anhydride (MA) and the effect of esterification of MA was studied on swelling properties in terms of absorption of water, at ambient temperature, and steam. It was found that the steam penetrates more within lesserperiod of time than water at ambient temperature. Untreated fiber composites show more absorption of steam and water in comparison to MA‐treated fiber composites. The more absorption of water was found in hemp fiber composites and less in sisal fiber composites. Steam absorption in MA‐treated and untreated fiber composites are higher than the water absorption in respective fiber composites. The natural fiber/polymer composites containing low amount of fibers show less absorption of steam and water at ambient temperature than the composites containing more amount of fibers in respective fiber composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Pretreatments of natural fibers and their application as reinforcing material in polymer composites—A review

In recent years, natural fibers reinforced composites have received much attention because of their lightweight, nonabrasive, combustible, nontoxic, low cost and biodegradable properties. Among the various natural fibers; flax, bamboo, sisal, hemp, ramie, jute, and wood fibers are of particular interest. A lot of research work has been performed all over the world on the use of natural fibers as a reinforcing material for the preparation of various types of composites. However, lack of good interfacial adhesion, low melting point, and poor resistance towards moisture make the use of natural fiber reinforced composites less attractive. Pretreatments of the natural fiber can clean the fiber surface, chemically modify the surface, stop the moisture absorption process, and increase the surface roughness. Among the various pretreatment techniques, graft copolymerization and plasma treatment are the best methods for surface modification of natural fibers. Graft copolymers of natural fibers with vinyl monomers provide better adhesion between matrix and fiber. In the present article, the use of pretreated natural fibers in polymer matrix‐based composites has been reviewed. Effect of surface modification of natural fibers on the properties of fibers and fiber reinforced polymer composites has also been discussed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Injection molded noil hemp fiber composites: Interfacial shear strength,fiber strength,and aspect ratio

Noil hemp fiber‐reinforced polypropylene composites were fabricated using intermixer and injection molding machines. X‐ray microtomography and Weibull statistical methods were employed to characterize the aspect ratio distributions of noil hemp fibers in the polypropylene matrices. The influence of fiber content (0–40 wt%) and compatibilizer addition (5 wt%) on IFSS (interfacial shear strengths) was evaluated by means of the modified Bowyer and Bader model. The evaluated IFSSs decreased from 9.7 to 7.2 MPa as the fiber content increased from 10 to 40 wt%. Also, the outcomes indicated increases to IFSSs for the maleic anhydride grafted polypropylene (MAPP)‐coupled composites than uncoupled ones. They were used to predict theoretical tensile strength of the composites. A good agreement has been found between the theoretical and the experimental tensile strengths of composites indicating that the developed model has excellent capability to predict the tensile strength of noil hemp fiber reinforced polypropylene composites. Ultimately, the influences of interfacial shear strength; fiber strength and fiber aspect ratio were investigated using the developed model to predict composite tensile strengths. POLYM. COMPOS., 213–220, 2016. © 2014 Society of Plastics Engineers     

Moisture absorption properties of wood‐fiber‐reinforced recycled polypropylene matrix composites

To reduce the moisture absorption of wood‐fiber‐reinforced recycled plastic composites (WRPCs), a coupling agent (KH550), methyl methacrylate (MMA), and maleic anhydride (MA) were used to modify the wood fibers. The surface‐treated wood fibers were mixed with recycled polypropylene and processing agents to fabricate the WRPCs. The mechanical properties and moisture absorption behavior of the WRPCs were determined. The results showed that the three surface treatment methods could effectively reduce the moisture absorption and thickness swelling of WRPCs. In Comparison to the properties of untreated wood‐fiber‐reinforced WRPCs, the moisture absorption ratio of WRPCs with wood fibers treated by MMA, KH550, and MA was reduced by 31.4%, 49.8%, and 38.2%, respectively, and the tensile strength was increased by 22.1%, 26.3%, and 4.2%, respectively. The impact toughness of the WRPCs was increased by 36.2% KH550 treatment and 19.2% for MMA treatment but was decreased by 4.2% for MA treatment. Coupling treatment of the wood fibers was the best way to reduce the moisture absorption of WRPCs, and this kind of WRPC possessed the best comprehensive properties. J. VINYL ADDIT. TECHNOL., 2010. © 2009 Society of Plastics Engineers     

One‐step green treatment of hemp fiber used in polypropylene composites

In this article, an eco‐friendly and cost effective surface treatment method is proposed for hemp fiber, enabling fabrication of hemp fiber/polypropylene (PP) composites, which show better mechanical properties than the PP composites containing untreated or alkali treated hemp fiber. Various techniques, such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), moisture analysis, and differential scanning calorimetry (DSC), are employed for the characterization of hemp fiber and polymer composites interface. Based on these results, the conventional alkali treatment of hemp fiber results in the damage of elementary fiber by eliminating parts of lignin and hemicellulose, which could be the reason for the decline of mechanical properties for the resulted polymer composites. On the contrary, water treatment cleans the fiber surface by effectively removing the water‐soluble polysaccharides while ensures minimum degradation on elementary fiber structure, which contributes to the improved mechanical properties of final polymer composites: the Young's modulus, fracture stress and fracture strain were enhanced by 3.66, 7.86, and 14.6%, respectively, when compared with untreated fiber reinforced composites. POLYM. COMPOS., 37:385–390, 2016. © 2014 Society of Plastics Engineers     

Injection‐molded short hemp fiber/glass fiber‐reinforced polypropylene hybrid composites—Mechanical,water absorption and thermal properties

Natural fiber‐based thermoplastic composites are generally lower in strength performance compared to thermoset composites. However, they have the advantage of design flexibility and recycling possibilities. Hybridization with small amounts of synthetic fibers makes these natural fiber composites more suitable for technical applications such as automotive interior parts. Hemp fiber is one of the important lignocellulosic bast fiber and has been used as reinforcement for industrial applications. This study focused on the performance of injection‐molded short hemp fiber and hemp/glass fiber hybrid polypropylene composites. Results showed that hybridization with glass fiber enhanced the performance properties. A value of 101 MPa for flexural strength and 5.5 GPa for the flexural modulus is achieved from a hybrid composite containing 25 wt % of hemp and 15 wt % of glass. Notched Izod impact strength of the hybrid composites exhibited great enhancement (34%). Analysis of fiber length distribution in the composite and fracture surface was performed to study the fiber breakage and fracture mechanism. Thermal properties and resistance to water absorption properties of the hemp fiber composites were improved by hybridization with glass fibers. Overall studies indicated that the short hemp/glass fiber hybrid polypropylene composites are promising candidates for structural applications where high stiffness and thermal resistance is required. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2432–2441, 2007     

Poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)‐based biocomposites reinforced with kenaf fibers

Biodegradable thermoplastic‐based composites reinforced with kenaf fibers were prepared and characterized. Poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV), produced by bacterial fermentation, was selected as polymeric matrix. To improve PHBV/fibers adhesion, low amount of a proper compatibilizing agent, obtained by grafting maleic anhydride onto PHBV, was added during matrix/fibers melt mixing (reactive blending). When compared with uncompatibilized composites, the presence of the compatibilizer induces a stronger interfacial adhesion and a more pronounced improvement of the mechanical properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

The Compatibilizing Effect of Maleic Anhydride on Swelling Properties of Plant-Fiber-Reinforced Polystyrene Composites

In this work the fibers of banana, hemp, and sisal are employed as fillers for the formation of wood polymer composites with polystyrene in the different ratios of 40:60 and 45:55 (wt/wt), respectively. These fibers were esterified with maleic anhydride, and the effect of maleic anhydride was studied on absorption of steam and water at ambient temperature in wood polymer composites. Untreated fiber composites show more absorption of steam in comparison to maleic anhydride (MA)–treated fiber composites. The absorption of water increases with the increase in time from 2–30 h in all untreated fiber composites. The maximum absorption of water was found in hemp fiber composites and the minimum in sisal fiber composites. The maleic anhydride esterified fiber composites showed less absorption of water than the untreated fiber composites. Steam absorption in MA treated and untreated fiber composites is higher than the water absorption in respective fiber composites. The wood polymer composites containing low amount of fiber shows less absorption of steam and water at ambient temperature than the composites containing a greater amount of fiber in respective fiber composites.     

Preparation and characterization of poly[(butylene succinate)‐co‐(butylene adipate)]/carbon nanotube‐coated silk fiber composites

Biodegradable composites consisting of aliphatic polyesters (poly[(butylenes succinate)‐co‐(butylenes adipate)] (PBSA)) and Bombyx mori silk fibers coated with carbon nanotubes (CNTs) were prepared by melt compression molding. The mechanical properties of PBSA were enhanced by the incorporation of a small amount (3 wt%) of CNT‐coated silk fibers, while allowing its potential biodegradability to be retained, which could make these composites good candidates for commodity materials such as general‐purpose plastics. This improvement is attributed to the interactions between PBSA and CNT‐coated silk fibers in the composites. The average interfacial shear strength of the composites consisting of CNT‐coated silk fibers and PBSA matrix was 1.7 MPa, as measured by the microbond droplet test, while that of composites consisting of pure silk fibers and PBSA was only 1.1 MPa. The morphology of the CNT‐coated silk fiber‐reinforced composites was observed using scanning electron microscopy. Copyright © 2007 Society of Chemical Industry     

A comparative study on viscoelastic properties of polymeric composites measured by a longitudinal free vibration non-destructive test and dynamic mechanical thermal analysis

In this study, viscoelastic properties of polymeric composites were investigated through a non-destructive test (NDT) method based on longitudinal free vibration. First, three different polyester composites reinforced separately with carbon, glass, and hemp fibers, as well as, one polyester composite sample reinforced with poplar wood powder were manufactured via pultrusion and hand lay-up methods, respectively. In the proposed resonant free vibration non-destructive method, each rod-shaped test specimen was hit by a hammer at one end of specimen and immediately the acoustic response of the specimen was recorded by a microphone at the other end of the sample. Subsequently, the recorded sounds were analysed using fast Fourier transform technique. Then, frequency of the first mode of vibration for each composite specimen was utilised to calculate modulus of elasticity. Further, decrement in vibration energy as a function of time was examined to obtain loss parameter (tan ??) of the provided composites. Moreover, parameters (i.e., elastic modulus and tan ??) were also compared with those determined by dynamic mechanical thermal analysis (DMTA). It is found that the results obtained from the examined non-destructive test method are in consistent with those measured by DMTA approach, providing reliable, accurate and quick responses.     

Mechanical properties of wood plastic composite panels made from waste fiberboard and particleboard

The possibility of producing wood‐plastic panels using a melt blend/hot press method was studied in this research. The studied panels were compared with conventional medium density fiberboard (MDF) and particleboard (PB) panels. Wood‐plastic panels were made from high density polyethylene (as resin) and MDF waste and PB waste (as natural fiber) at 60, 70, and 80% by weight fiber loadings. Nominal density and dimensions of the panels were 1 g/cm³ and 35 × 35 × 1 cm³, respectively. Mechanical properties of the panels including flexural modulus, flexural strength, screw and nail withdrawal resistances, and impact strength were studied. Results indicated that the mechanical properties of the composites were strongly affected by the proportion of the wood flour and polymer. Maximum values of flexural modulus of wood plastic panels were reached at 70% fiber content. Flexural strength, screw and nail withdrawal resistance, and impact strength of wood plastic composites declined with the increase in fiber content from 60 to 80%. This was attributed to the lack of compatibility between the phases. The produced panels outperformed conventional PB panels regarding their mechanical properties, which were acceptable when compared with MDF panels as well. The best feature in the produced panels was their screw withdrawal resistance, which is extremely important for screw joints in cabinet making. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers