Broom fibers as reinforcing materials for polypropylene-based composites

Broom fibers have been used as reinforcement for the conventional polypropylene (iPP) and a maleate modified one (iPPMA). A conventional alkaline treatment and a steam explosion extraction process were applied to obtain the cellulosic material from broom branches. Composites were prepared by melt mixing materials with different weight percentages of broom fibers. Also ternary blends (iPPMA/iPP/broom fibers 5/45/50 wt) were obtained to examine the possibility of utilizing the maleate polypropylene as a compatibilizing agent. The fibers and the composites were thermally, morphologically, and mechanically characterized. Water absorption tests, to examine the behavior of these materials in wet conditions, were also performed. Particular attention was addressed to the study of the fiber/matrix interfacial adhesion. The results showed that the iPPMA-based composites, reinforced with alkaline extracted broom fibers, present specific mechanical properties competitive with those of the homologous polypropylene-based materials reinforced with short glass fibers. The ternary blends gave similar properties to those of the corresponding whole iPPMA-based composites. It is considered that the esteric linkage between the cellulose —OH, and the maleic anhydride groups grafted on the polypropylene backbone is greatly responsible for the similarity in the properties. In spite of better adhesion observed in the samples reinforced by the steam-exploded fibers, less improvement of the mechanical properties was observed, owing to significant damage of the structure of the fibers during the steam explosion process. A general decrease of mechanical properties is observed in normal polypropylene-based composites. The results are also supported by the water absorption tests: whereby the iPPMA-based composites showed good capability to return their dry properties when kept in an oven after wetting for many days. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1077–1089, 1998     

Regenerated and graft copolymer fibers from steam-exploded wheat straw: Characterization and properties

Steam explosion treatment has been proven to effectively induce such marked modifications to the chemical and supramolecular structure of wheat straw cellulose as to make this cellulose a suitable raw for dissolving processes. Regenerated and poly(acrylonitrile) (PAN) and poly(methyl methacrylate) (PMMA) grafted wheat straw fibers obtained on the laboratory scale were characterized by various techniques (X-ray diffraction, cross polarization-magic angle spinning (CP-MAS) ¹³C nuclear mag-netic resonance and vibrational spectroscopy, scanning electron microscopy, differential scanning calorimetry), and the relationships between the morphological–structural features and physicomechanical and end-use properties have been evidenced. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:961–974, 1998     

Comparison between dew‐retted and enzyme‐retted flax fibers as reinforcing material for composites

Two kinds of retted Canadian linseed flax fibers, dew‐retted (F1) and enzyme‐retted flax fibers (F2) were characterized in detail for their applications in composites, such as retting degree, thermal stability, tensile strength, and interfacial behavior in polypropylene (PP) matrix. It's clear from Scanning Electron Micrograph that the aspect ratio of F2 was much higher than that of F1 in the light of their separated elementary fibers in most cases. Instead, the elementary fibers of F1 remained tightly bundled into technical fiber wrapping with more non‐cellulose portions. This reflected its lower retting degree and resulted in its lower thermal stability. Single fiber tensile test and single fiber pull‐out test were used to evaluate the fiber tensile properties and fiber/PP interfacial shear strength, respectively. Better retting degree and fewer damages on F2 endowed F2 better tensile property. Consequently, higher aspect ratio, retting degree, and tensile strength proved F2 to be a kind of better reinforcing material than F1 for composites. POLYM. ENG. SCI., 2012. 2011 published by Society of Plastics Engineers     

Conifer fibers as reinforcing materials for polypropylene‐based composites

Conifer fibers were used to reinforce polypropylene (PP). To improve the compatibility between the conifer fibers and the PP matrix, the fibers were either grafted with maleated PP (MAPP), treated by adding MAPP, or mixed with ethylene/propylene/diene terpolymer (EPDM). The treatments resulted in improved processing, as well as improvements in the thermal and mechanical properties of the resultant composites compared with the composites filled with untreated conifer fibers. Moreover, MAPP grafting and MAPP treating displayed more obvious benefits than EPDM treating in terms of thermal properties, processing flowability, and tensile strength improvements. EPDM treating also produced more significant benefits than either MAPP grafting or MAPP treating in terms of impact strength and tensile elongation improvements. These improvements were attributed to surface coating of the fibers when EPDM was used. In addition, the effect of the concentration of the conifer fibers on the properties of the composites and the difference between MAPP grafting and MAPP treating were evaluated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2833–2841, 2001     

Grape stalk fibers as reinforcing filler for polymer composites with a polystyrene matrix

Lignocellulosic fibers have been one of the most used reinforcements for different types of composites. In this context, grape stalks—often discarded in landfills—can be a potential reinforcement for composites. The present study aimed to incorporate in natura and alkali treated grape stalks into the polystyrene (PS) matrix. Initially, the grape stalks were treated with NaOH and 10, 20, and 30 wt % of stalks were added into the PS matrix. The alkaline treatment of the grape stalk fibers promoted the removal of hemicellulose and the partial removal of lignin, thus increasing the surface roughness and crystallinity index of the fibers. An improvement in the mechanical and dynamic-mechanical properties and an increase in the maximum degradation temperature of the composites were observed. In conclusion, the use of grape stalks is a promising alternative for reinforcing composites, and, in addition, a more proper destination can be given to this type of residue. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47427.     

Recycled old newsprint fibers as a reinforcing filler in molded polyester composites

Using old newsprint (ONP) fibers as reinforcing filler in polyester (PE) composite has been studied. Using ONP fibers in PE composite resulted in a decrease in modulus of rupture (MOR) and an increase in modulus of elasticity (MOE) and tensile strength as compared with a neat PE composite. Also, water absorption and thickness swelling were increased as a result of using ONP fibers in the composite. Acetylation, steaming, and esterification (using maleic anhydride) of ONP fibers were performed to improve the dimensional stability of the produced composite. Acetylation and steaming of ONP fibers resulted in a decrease in the thickness swelling of the produced composites; MOR, MOE, and tensile strength were also decreased as a result of these treatments. Esterification of ONP fibers using maleic anhydride resulted in a decrease in thickness swelling of the produced composite and, at the same time, an increase in MOR, MOE, and tensile strength. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2018–2023, 2001     

Wood fibers as reinforcing fillers for polyolefins

Wood pulp fibers possess strength and modulus properties which compare favorably with glass fibers when the differences in fiber densities are considered. Softwood pulp fibers with fiber aspect ratios near 100 are readily dispersed into high-density polyethylene or isotactic polypropylene with the aid of carboxyic dispersing agents to form mixtures containing 50 weight-percent wood pulp which can be readily injection molded. The mechanical properties of the molded specimens were similar for all types of pulp including Kraft (bleached and unbleached), mechanical and chemical-mechanical pulps, waste pulps, and reclaim newspapers. Comparisons of the stiffness/weight efficiencies revealed that pulp composites equal or exceed the stiffness of most traditional materials of construction including steel, aluminum, glass-fiber composites, and talefilled polyolefins, while retaining a major material cost advantage. The measured strength values of the pulp composites were less than the theoretically predicted values due to the presence of voids created by the formation of volatiles during processing. Mechanical pulps which were available in dry form were preferred because of lower cost and ease of handling. Wood fibers are non-abrasive so that relatively large concentrations may be incorporated into polyolefins without causing serious machine wear during mixing and fabrication.     

Understanding external plasticization of melt extruded PHBV–wheat straw fibers biodegradable composites for food packaging

The objective of this work is to get further knowledge on the external plasticization mechanisms of melt extruded polyhydroxyl‐3‐butyrate‐co?3‐valerate (PHBV) when combined with wheat straw fibers (WSF). Different types of biodegradable substances, all authorized for food contact according to the European regulation, i.e., acetyltributyl citrate (ATBC), glycerol triacetate (GTA) and (PEG) at different molecular weights, were tested at different percentages (5, 10 and 20 wt %). Thermal and mechanical characterization of PHBV/plasticizer blends showed that a significant plasticizing effect was obtained using hydrophobic substances such as ATBC and GTA, with an increase of the elongation at break from 1.8% up to about 6% for an additive content of 10 wt %. However, the incorporation of WSF in plasticized PHBV led to a dramatic decrease in the elongation at break of composites, neutralizing the increase of this parameter by the addition of the plasticizers. The stress at break of plasticized films was also significantly decreased by the introduction of fibers. Such a loss of ductility was mainly explained by the occurrence of microscopic defects in the materials induced by the presence of fibers and to a poor adhesion at the fiber/matrix interface. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41611.     

Characterization of nanocellulose from Indica rice straw as reinforcing agent in epoxy-based nanocomposites

The extraction of nanocellulose from agro-waste have received wide attention in nanocomposite technologies. This research unravels physico-chemical characteristics of cellulose from Malaysia Indica rice straw, and the derived cellulose nanocrystal (CNC) by hydrochloric acid (HCl) hydrolysis. The CNC was subjected to field emission scanning electron microscopy (FESEM) and/or transmission electron microscopy (TEM) and Fourier transformed infrared (FTIR) studies. Furthermore, X-ray diffraction (XRD) and small-angle X-ray scattering (SAXS) were compared with TEM for the CNC lateral crystal size. Subsequently, CNC reinforced epoxy laminates for Kevlar were prepared and tested for their tensile properties. While FTIR analysis confirmed the monoclinic cellulose structure of the isolated CNC, XRD, and SAXS were compared with TEM for the CNC lateral crystal size. Hydrolysis of the cellulose sample yielded 40.87% of CNC with 4.8 nm in width and a needle-shaped nature. The extracted CNC has relatively low crystallinity (56.12%) but interestingly low crystallite size with an average crystallite size of 1.69 nm (XRD) and 4.18 nm (SAXS). Furthermore, an addition of just 1 wt% of CNC to epoxy composite increased the strength of Kevlar by over 300% and the elastic modulus by nearly three-fold. Nanocellulose obtained from rice straw have great potential as reinforcing agents for the manufacture of nanocomposites.     

Chemical surface modification of wheat straw fibers for polypropylene reinforcement

The use of natural materials has grown in the last years in the plastics industry. Natural lignocellulose fibers derived from agricultural waste present potential to be used as a replacement for glass fibers for polymer reinforcement, leading to lower CO₂ footprint products. However, cellulose fibers are hydrophilic and polar and as a result of that, incompatible with hydrophobic polymers such as polypropylene. For this reason, a surface modification on the cellulose fiber is required. This work focuses on the modification of the cellulose fibers to improve the compatibility with polypropylene. Wheat straw fibers derived from agricultural waste were scoured with the purpose to remove lignin, hemicellulose and pectin to facilitate the defibrillation. The fibers were then esterified using acetic anhydride. Thermal gravimetric tests have shown an increase in the thermal stability of the scoured and esterified cellulose fibers, from 246°C for untreated fibers to 292°C and 316°C, respectively. From mechanical tests results it could be seen that the tensile modulus of the composites with esterified cellulose fibers increased 57% compared with the neat PP. Flexural strength increased by 31% and flexural modulus by 70%. The use of esterified fibers led to an improvement of 79% in the impact strength compared with the neat PP. A better compatibilization between fibers and matrix could be seen using maleic anhydride modified polypropylene copolymer as compatibilizer, even with esterified fibers, probably due to residual hydroxyl groups still available on modified cellulose. POLYM. COMPOS., 37:2133–2141, 2016. © 2015 Society of Plastics Engineers     

Effects of wheat straw fiber content and characteristics,and coupling agent concentration on the mechanical properties of wheat straw fiber‐polypropylene composites

Wheat straw fiber‐polypropylene (PP) composites were prepared to investigate the effects of wheat straw fiber content (10, 20, 30, 40, and 50 wt %), fiber size (9, 28, and 35 mesh), and maleic anhydride grafted polypropylene (MAPP) concentration (1, 2, 5, and 10 wt %) on the static and dynamic mechanical properties of the wheat straw fiber‐PP composites in this study. The tensile modulus and strength of the composites increased linearly with increasing wheat straw fiber content up to 40%, whereas the elongation at break decreased dramatically to 3.78%. Compared with the composites made of the longer wheat straw fiber, the composites made of the fines (>35 mesh) had a slightly higher tensile strength of 31.2 MPa and tensile elongation of 5.39% at break. With increasing MAPP concentration, the composites showed an increase in tensile strength, and the highest tensile strength of 34.0 MPa occurred when the MAPP concentration reached 10 wt %. As wheat straw fiber content increased from 0 to 40%, the flexural modulus of the composites increased gradually from 1335 to 3437 MPa. The MAPP concentration and wheat straw fiber size distribution had no appreciable effect on the static flexural modulus of the composites. The storage flexural modulus of the composites increased with increasing wheat straw fiber content. The scanning electron microscopy (SEM) observation on the fracture surface of the composites indicated that a high wheat straw fiber content (>30 wt %) resulted in fiber agglomeration and a reduction in interfacial bonding strength. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of microwave radiation induced graft copolymers and their applications as reinforcing material in phenolic composites

Flax fiber was modified through grafting of binary vinyl monomers mixtures such as methyl methacrylate (MMA)/vinyl acetate (VA), MMA/acrylamide (AAm), and MMA/styrene (Sty) under the influence of microwave radiations. 24.64% grafting was found at 210 W microwave power under optimum reaction conditions. Graft copolymers obtained were characterized with FTIR spectroscopy, scanning electron microscopy, and TGA/DTA techniques. Graft copolymers were found to be moisture retardant with better tensile strength. Phenolic composites using graft copolymers vis‐à‐vis flax as reinforcing material were subjected for the evaluation of different mechanical properties such as wear resistance, tensile strength, compressive strength, modulus of rupture (MOR), modulus of elasticity (MOE), and stress at the limit of proportionality (SP). Composites reinforced with graft copolymers showed better mechanical properties in comparison to composites reinforced with flax. Phenolic composites reinforced with Flax‐g‐poly(MMA/Sty) showed maximum wear resistance followed by reinforcement with flax, Flax‐g‐poly (MMA/AAm), and Flax‐g‐poly(MMA/VA). Composites reinforced with Flax‐g‐poly(MMA/Sty) and flax fibers have been found to show 150 N tensile strength with extension of 3.94 and 2.17 mm, respectively. It has also been found that composites reinforced with Flax‐g‐poly(MMA/Sty) showed maximum compressive strength (1,000 N) with compression of 3.71 mm in comparison to other graft copolymers and flax fibers reinforcement. Reinforcement of phenolic resin with Flax‐g‐poly(MMA/Sty) and flax fibers could improve the MOR and MOE. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Green composites based on wheat gluten matrix and posidonia oceanica waste fibers as reinforcements

In this work, green composites from renewable resources were manufactured and characterized. A fibrous material derived from Posidonia oceanica wastes with high cellulose content (close to 90 wt% of the total organic component) was used as reinforcing material. The polymeric matrix to bind the fibers was a protein (wheat gluten) type material. Composites were made by hot‐press molding by varying the gluten content on composites in the 10–40 wt% range. Mechanical properties were evaluated by standardized flexural tests. Thermo‐mechanical behavior of composites was evaluated with dynamic mechanical analysis (torsion DMA) and determination of heat deflection temperature. Morphology of samples was studied by scanning electronic microscopy and the water uptake in terms of the water submerged time was evaluated to determine the maximum water uptake of the fibers in the composites. Composites with 10–40 wt% gluten show interesting mechanical performance, similar or even higher to many commodity and technical plastics, such as polypropylene. Water resistance of these composites increases with the amount of gluten. Therefore, the sensitiveness to the water of the composites can be tailored with the amount of gluten in their formulation. POLYM. COMPOS., 34:1663–1669, 2013. © 2013 Society of Plastics Engineers     

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     

Environment-friendly deposition of SiCN interlayer for reinforcing carbon fibers in C/SiC composites

Several C/SiC composites with no interlayer, single pyrocarbon (PyC) interlayer and PyC/SiCN interlayer were fabricated by polymer infiltration and pyrolysis process. The microstructure and mechanical properties were investigated. The results verified that SiCN interlayer was formed on carbon fibers. Both bulk density and flexural stress of C/SiC composite with PyC/SiCN interlayer were slightly higher than composite fabricated with single PyC interlayer. When the weight fraction of SiCN interlayer in the composite was about 18 wt%, the flexural stress of the composite was enhanced to 416 MPa from 352 MPa for composite with single PyC interlayer. The observations of pulled-out fibers on fracture surfaces revealed non-catastrophic fracture features for PyC/SiCN deposited C/SiC composite.     

Characterization of polymeric fibers as reinforcements of cement‐based composites

In this study, three polymeric fibers (nylon 66, polypropylene, and acrylic) were used to improve the flexural and tension strength of cementitious materials. To characterize the performance of these fibers in a cement matrix, scanning electron microscopy, optical microscopy, dynamic mechanical analysis, tensile strength testing, and alkali resistance test were employed. The performance of cement‐based composites containing the fibers was evaluated with a flexural strength test. The results indicated that the flexural strength increased with an increasing number of interfacial interactions between the fibers and cement. This finding was supported by dynamic mechanical analysis data. This has great application potential for fibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polypropylene-grafted nanoparticles as a promising strategy for boosting physical properties of polypropylene-based nanocomposites

SiO₂ nanoparticles grafted to terminally hydroxylated polypropylene (PP-g-SiO₂) with different molecular weights were melt mixed with PP to prepare a series of PP/PP-g-SiO₂ nanocomposites. PP/PP-g-SiO₂ offered several advantages over pristine PP and PP/unmodified SiO₂ such as highly uniform dispersion up to 10 wt.-%, +200–400% faster crystallization and +30% increments for both the Young's modulus and the tensile strength without largely sacrificing the melt viscosity of PP. We concluded that grafted chains act as crystallization nuclei and co-crystallize with matrix chains to make PP-g-SiO₂ nanoparticles as a physical cross-linker between lamellae, while the linkage disappears in melt and grafted chains minimize the cohesive attraction between nanoparticles.     

Modified fibers for polymer composites with improved mechanical properties

In this paper, a new composite material, AEG, which was developed in our laboratory by catalytic grafting polymerization of ethylene on asbestos fibers, was used to improve the properties of asbestos/HDPE composites. Tensile testing shows that the AEG modified asbestos/HDPE composites exhibit significantly higher tensile strength and elongation at break than the unmodified ones. Instrumented impact testing permits a detailed understanding of the modifying effect of AEG on impact properties. The records acquired during impact for the unmodified composites were truncated at the onset of initial fracture, showing a typical brittle cleavage fracture. In contrast, the records for the AEG modified composites showed an effective post-initial fracture behavior. The load at peak, the energy required to initiate and propagate the fracture, and the deformation during impact increase dramatically for the AEG modified composites. SEM micrographs of the fractured surfaces also demonstrate the difference in the morphology of the two composites.