Wood‐fiber/high‐density‐polyethylene composites: Compounding process

The compounding process directly influenced the compounding quality of wood–polymer blends and finally affected the interfacial bonding strength and flexural modulus of the resultant composites. With 50 wt % wood fiber, the optimum compounding parameters for the wood‐fiber/high‐density‐polyethylene blends at 60 rpm were a temperature of 180°C and a mixing time of 10 min for the one‐step process with a rotor mixer. The optimum compounding conditions at 90 rpm were a temperature of 165°C and a mixing time of 10 min. Therefore, a short compounding time, appropriate mixing temperatures, and a moderate rotation speed improved the compounding quality of the modified blends and the dynamic mechanical properties of the resultant composites. The melt torque and blend temperature followed a polynomial relationship with the loading ratio of the wood fiber. The highest melt torque and blend temperature were obtained with 50% wood fiber. The coupling treatment was effective for improving the compatibility and adhesion at the interface. The two‐step process was better than the one‐step process because the coupling agents were more evenly distributed at the interface with the two‐step process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2570–2578, 2004     

Extrusion processing of green biocomposites: Compounding,fibrillation efficiency,and fiber dispersion

The efficiency of twin‐screw extrusion process to fibrillate cellulose fibers into micro/nanosize in the same step as the compounding of green bionanocomposites of thermoplastic starch (TPS) with 10 wt % fibers was examined. The effect of the processing setup on micro/nanofibrillation and fiber dispersion/distribution in starch was studied using two types of cellulose fibers: bleached wood fibers and TEMPO‐oxidized cellulose fibers. A composite with cellulose nanofibers was prepared to examine the nanofiber distribution and dispersion in the starch and to compare the properties with the composites containing cellulose fibers. Optical microscopy, scanning electron microscopy, and UV/Vis spectroscopy showed that fibers were not nanofibrillated in the extrusion, but good dispersion and distribution of fibers in the starch matrix was obtained. The addition of cellulose fibers enhanced the mechanical properties of the TPS. Moisture uptake study revealed that the material containing TEMPO‐oxidized fibers had higher moisture absorption than the other composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39981.     

Effects of soaking and freezing on composites made from wood‐based fillers and biodegradable plastics

Biodegradable plastic composites were subjected to prolonged soaking and freezing treatments to assess the effects on the mechanical performance. Radiata pine flour and thermomechanical pulp fibers were used as fillers at various addition levels in three different commercial polymer matrices. Two were bioderived, one oil‐derived, each with different hydrophobicities. Depending on the nature of the biodegradable polymer matrix, the rates and extents of water uptake were found to be either enhanced or reduced by the wood‐derived fillers. Although the higher aspect ratio of the pulp fibers improved mechanical performance, relative to the wood flour, water uptake was also significantly enhanced in some cases. POLYM. COMPOS. 27:323–328, 2006. © 2006 Society of Plastics Engineers     

Biopolyamide hybrid composites for high performance applications

This study focuses on the performance characteristics of wood/short carbon fiber hybrid biopolyamide11 (PA11) composites. The composites were produced by melt‐compounding of the fibers with the polyamide via extrusion and injection molding. The results showed that mechanical properties, such as tensile and flexural strength and modulus of the wood fiber composites were significantly higher than the PA11 and hybridization with carbon fiber further enhanced the performance properties, as well as the thermal resistance of the composites. Compared to wood fiber composites (30% wood fiber), hybridization with carbon fiber (10% wood fiber and 20% carbon fiber) increased the tensile and flexural modulus by 168% and 142%, respectively. Izod impact strength of the hybrid composites exhibited a good improvement compared to wood fiber composites. Thermal properties and resistance to water absorption of the composites were improved by hybridization with carbon fiber. In overall, the study indicated that the developed hybrid composites are promising candidates for high performance applications, where high stiffness and thermal resistance are required. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43595.     

Highly compatible wood thermoplastic composites from lignocellulosic material modified in ionic liquids: Preparation and thermal properties

A study of converting chemically modified wood into thermoplastic materials was undertaken to develop a new technology platform for the effective utilization of wood‐based lignocellulosic materials. Highly substituted benzoylated spruce thermomechanical pulp (TMP) and lauroylated spruce TMP were used as components for thermoplastic composites of poly(styrene) and poly(propylene). Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA) were used to characterize the interfacial morphology and thermal properties of the resultant composite filaments. The coupling of the interfacial morphology effort and that of torque analysis applied during processing indicated that the thorough modification of wood fibers by benzoylation and/or lauroylation reactions can improve the compatibility between the wood‐based lignocellulosic materials and poly(styrene) and poly(propylene). Thermal analysis showed that, with the addition of wood derivatives into poly(styrene) and poly(propylene) matrices, a slight decrease in their T_gs was observed. Furthermore, all of the prepared composites showed improved thermal stability, as revealed by TGA. The resultant thermoplastic wood composites exhibited good melting properties and were readily extruded into filaments or sheets. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The effect of maleic anhydride grafting efficiency on the flexural properties of polyethylene composites

Many authors have reported on the property enhancements possible by compounding high density polyethylene (HDPE) with fillers to produce composites. It is accepted that polyethylene combined with materials such as nanoclay or wood flour will not yield favorable properties unless a compatibilizing material is used to form a link. In this work, compatibilized HDPE was produced by grafting maleic anhydride (MA) to its backbone in a twin screw extruder using a peroxide initiated reactive process. Fourier transform infrared spectroscopy (FTIR) was used to examine the effects of varying peroxide and MA levels on the grafting percentage and it was found that a high percentage could be achieved. The gel content of each HDPE‐g‐MA batch was determined and twin bore rheometry analysis was carried out to examine the effects of crosslinking and MA grafting on the melt viscosity. These HDPE‐g‐MA compatibilizers were subsequently compounded with nanoclay and wood flour to produce composites. The composite materials were tested using a three point bending apparatus to determine the flexural modulus and strength and were shown to have favorable mechanical properties when compared with composites containing no compatibilizer. X‐ray diffraction (XRD) was used to examine the effects of grafted MA content on the intercalation and exfoliation levels of nanoclay composites. The results from XRD scans showed that increased intercalation in polymer nanoclay composites was achieved by increasing the grafted MA content. This was confirmed using a scanning electron microscope, where images produced showed increased levels of dispersion and reductions in nanoclay agglomerates. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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     

Effects of nanoclay and coupling agent on the physico‐mechanical,morphological, and thermal properties of wood flour/polypropylene composites

This article presents the effects of coupling agent and nanoclay (NC) on some properties of wood flour/polypropylene composites. The composites with different NC and maleic anhydride grafted polypropylene (MAPP) contents were fabricated by melt compounding in a twin‐screw extruder and then by injection molding. The mass ratio of the wood flour to polymer was 40/60 (w/w). Results showed that applying MAPP on the surface of the wood flour can promote filler polymer interaction, which, in turn, would improve mechanical properties of the composite as well as its water uptake and thermal stability. Composite voids and the lumens of the fibers were filled with NC, which prevented the penetration of water by the capillary action into the deeper parts of composite. Therefore, the water absorption in composites fabricated using NC was significantly reduced. Scanning electron microscopy has shown that the treatment of composites with 5 wt% MAPP, promotes better fiber–matrix interaction, resulting in a few numbers of pull‐out traces. In all cases, the degradation temperatures shifted to higher values after using MAPP. The largest improvement on the thermal stability of composites was achieved when NC was added. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Preparation and characterization of functionalized low density polyethylene matrix biocomposites

The incorporation of cellulosic fibers into polyethylene matrices was studied in this work, by dispersion of fluff pulp from maritime pine in a hot polymer solution, followed by co‐precipitation of the solid components by cooling at room temperature. The above method was found suitable for proper wetting and dispersion of fibers in the polymeric matrix, as compared with melt compounding. Unmodified low density polyethylene [LDPE], modified LDPE with maleic anhydride grafted linear low density polyethylene [M‐LLDPE] and a copolymer of acrylic acid and n‐butyl acrylate polyethylene [(AA/n‐BA)‐LDPE], were used as matrices for the preparation of fiber reinforced composites. The thermal properties of these composites were determined using differential scanning calorimetry and thermogravimetric analysis. The incorporation of cellulosic fibers results in a decrease of the crystallinity of the polymer matrix, as they act as inert material. In addition, the appropriate tests were run in order to determine the density and tensile properties of the composite specimens prepared by compression molding, with filler content ranging from 10 to 40% (w/w). Composites based on modified LDPE showed improved mechanical properties. The Takayanagi model, applied to predict the Young's modulus of composites, was in very good agreement with the experimental data obtained in this work. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Crystallization,mechanical properties,and enzymatic degradation of biodegradable poly(ε‐caprolactone) composites with poly(lactic acid) fibers

Biodegradable polymer composites based on poly(ɛ‐caprolactone) (PCL) and poly(lactic acid) (PLA) fibers were prepared by melt compounding. The effects of PLA fibers on the crystallization, mechanical properties, and enzymatic degradation of PCL composites were investigated. The addition of PLA fibers enhanced the crystallization of PCL due to the heterogeneous nucleation effect of fibers. However, the final crystallinity of the PCL in the composites was little changed in the presence of PLA fibers. With the addition of PLA fibers, significant improvement in storage modulus (E′) of PCL in the composites was achieved. A significant increase in E′ was 173% for the composites as compared to that of the neat PCL at 20°C. With the increase in PLA fibers content, the PCL composites showed decreased elongation and strength at break; however, the tensile yield strength and modulus were increased significantly, indicating that PCL was obviously reinforced by adding PLA fibers. Although the PLA fibers retarded the enzymatic degradation of PCL, it was possible to be completely degraded without much degradation time for PCL blending with suitable amounts of PLA fibers. POLYM. COMPOS., 34:1745–1752, 2013. © 2013 Society of Plastics Engineers     

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.     

Enhanced oil resistance and mechanical properties of nitrile butadiene rubber/lignin composites modified by epoxy resin

This is probably the first report on developing nitrile butadiene rubber (NBR) composites with enhanced performance s via lignin bridged epoxy resin in the rubber matrix. NBR/lignin masterbatch has been prepared through latex‐compounding method, and then epoxy resin (F51) was added in the NBR/lignin compounds by the melt compounding method. Lignin‐epoxy resin networks were synthesized in situ during the curing process of rubber compounds through epoxide?hydroxyl reactions. Compared with lignin filler, lignin‐F51 networks showed an improved oil resistance ability and led to increased mechanical properties, crosslinking density, and thermal stability of the rubber composites. This method provides a new insight into the fabrication of novel interpenetrating polymer networks in rubber composites and enlarges the potential applications of lignin in high performance rubber composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42922.     

Fabrication and mechanical properties of glass fiber‐reinforced wood plastic hybrid composites

To fully utilize the resource in the municipal solid waste (MSW) and improve the strength and toughness of wood plastic composites, glass fiber (GF)‐reinforced wood plastic hybrid composites (GWPCs) were prepared through compounding of recycled high‐density polyethylene (HDPE) from MSW, waste wood fibers, and chopped GF. Mechanical tests of GWPCs specimens with varying amounts of GF content were carried out and the impact fractured surface of GWPCs was observed through scanning electron microscope (SEM). The tensile strength of GWPCs and the efficiency coefficient values were predicted by Kelly‐Tyson method. The results indicated that the tensile strength and impact strength of GWPCs could be improved simultaneously by adding type L chopped GF (L‐GF), and would be dropped down when type S chopped GF (S‐GF) was included. The tensile strength of GWPCs was well accordant with the experimental result. The efficiency coefficient values of S‐GF and L‐GF are ?0.19 and 0.63, respectively. Inspection of SEM micrographs indicated that L‐GF had achieved full adhesion with the plastic matrix through addition of maleic anhydride‐g‐polyethylene. The main fracture modes of GWPCs included pullout of GF, broken of matrix, and interfacial debonding. Because of the synergistic effects between hybrid components in GF/wood fiber/HDPE hybrid system, a special 3D network microstructure was formed, which was the main contribution to the significant improvement in the tensile strength and impact strength of L‐GF‐reinforced hybrid composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Microcellular Foamed Wood‐Plastic Composites by Different Processes: a Review

Wood fiber reinforced polymer composites represent a relatively small but rapidly growing material class, extensively applied in interior building applications and in the automotive industry. The polymer‐wood fiber composites utilize fibers as reinforcing filler in the polymer matrix and are known to be advantageous over the neat polymers in terms of the materials cost and mechanical properties such as stiffness and strength. Wood fiber reinforced polymer composites are microcellularly processed to create a new class of materials with unique properties. Most manufacturers are evaluating new alternatives of foamed composites that are lighter and more like wood. Foamed wood composites accept screws and nails like wood, more so than their non‐foamed counterparts. They have other advantages such as better surface definition and sharper contours and corners than non‐foamed profiles, which are created by the internal pressure of foaming. This paper represents a review on microcellular wood fiber reinforced polymer composites obtained by different processes (batch, injection molding, extrusion, and compression molding process) and includes an overview of foaming agents (physical and chemical) and the foaming of wood fiber‐polymer composites (changes in phase morphology, formation of polymer‐gas solution, cell nucleation, and cell growth control).

     

Kinetic and thermodynamic control in conductive PP/PMMA/EAA carbon black composites

Multiphase polymer blends provide unique morphologies to reduce the percolation concentration and increase conductivity of carbon‐based polymer composites via selective distribution of the conductive filler. In this work, the kinetic and thermodynamic effects on a series of multiphase conductive polymer composites were investigated. The electrical conductivity of carbon black (CB)‐filled conductive polymer blend composites comprising polypropylene, poly(methyl methacrylate), and ethylene–acrylic acid were determined as a function of compounding sequence and annealing time. Kinetic and thermodynamic parameters were found to influence the conductivity. Phase morphology and conductivity at short annealing times were influenced by the compounding sequence where the CB was added after being premixed with one of the polymer components or directly added to the three‐component polymer melt. However, they were thermodynamically driven at longer annealing times; the resistivity was found to decrease by a statistically significant amount to similar levels for all the composite systems with increasing annealing time. The increase in conductivity at longer annealing times was determined to be the result of changes in the phase morphology from sea‐island, dispersed microstructure to a tri‐continuous morphology rather than change in localization of CB, given that the CB was found to be entirely located in the EAA phase even at short annealing times (and independent of compounding sequence), where the conductivity was not measurable. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42134.     

Effect of lactic acid chain length on thermomechanical properties of star‐LA‐xylitol resins and jute reinforced biocomposites

Star‐shaped bio‐based resins were synthesized by direct condensation of lactic acid (LA) with xylitol followed by end‐functionalizing of branches by methacrylic anhydride with three different LA chain lengths (3, 5 and 7). The thermomechanical and structural properties of the resins were characterized by ¹³C NMR, Fourier transform IR spectroscopy, rheometry, DSC, dynamic mechanical analysis (DMA), TGA and flexural and tensile tests. An evaluation of the effect of chain length on the synthesized resins showed that the resin with five LAs exhibited the most favorable thermomechanical properties. Also, the resin's glass transition temperature (103 °C) was substantially higher than that of the thermoplast PLA (ca 55 °C). The resin had low viscosity at its processing temperature (80 °C). The compatibility of the resin with natural fibers was investigated for biocomposite manufacturing. Finally, composites were produced from the n5‐resin (80 wt% fiber content) using jute fiber. The thermomechanical and morphological properties of the biocomposites were compared with jute‐PLA composites and a hybrid composite made of the impregnated jute fibers with n5 resin and PLA. SEM and DMA showed that the n5‐jute composites had better mechanical properties than the other composites produced. Inexpensive monomers, good thermomechanical properties and good processability of the n5 resin make the resin comparable with commercial unsaturated polyester resins. © 2017 Society of Chemical Industry     

Preparation and characterization of wood‐(nylon 12) composites

The melting temperature of nylon 12 is lower than the degradation temperature of wood, which makes the preparation of wood‐(nylon 12) composites through a regular compounding/compression molding process possible. Results indicated that wood‐(nylon 12) composites had higher modulus of rupture, higher modulus of elasticity, and higher tensile strength than nylon 12, wood‐polypropylene (PP) composites, and wood‐high density polyethylene (HDPE) composites, respectively. Wood‐(nylon 12) composites also had higher thermal stability than wood‐PP composites and wood‐HDPE composites. Acting as a nucleating agent, wood increased the crystallization temperature and the degree of crystallinity of nylon 12 in wood‐(nylon 12) composites. The superior mechanical properties of wood‐(nylon 12) composites were ascribed to the good interfacial adhesion between wood and nylon 12 and the increased transcrystallinity of nylon 12 by wood. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:270–276, 2007     

The influences of fiber feature and polymer melt index on mechanical properties of sugarcane fiber/polymer composites

The fiber characteristics (i.e., the fiber type, morphology, and dimension) and polymer melt flow index (MFI) significantly affected mechanical properties of sugarcane fiber/HDPE composites. The length and diameter of sugarcane fibers followed a lognormal distribution before and after compounding. The long fibers had a significant reduction in the dimension and aspect ratio during compounding. However, the short fibers had close values in these two properties before and after compounding. For the resultant sugarcane fiber/polymer composites, the HDPE resins with a low MFI value presented high tensile and impact strengths. Because of high sugar content, the pure rind fiber had a poor performance as filler in the HDPE resins with respect to the raw bagasse fiber and alkali‐extracted bagasse fiber. On the other hand, the aspect ratio was proportional to the mechanical performance of the fibers in the HDPE resins. As a result, the fibers with a large aspect ratio and low sucrose content improved the strength properties of the resultant composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5607–5619, 2006     

Poly(trimethylene terephthalate) nanocomposite fibers comprising different organoclays: Thermomechanical properties and morphology

Poly(trimethylene terephthalate) (PTT) nano composites were synthesized by in situ polymerization at high temperature with two thermally stable organoclays: 1,2‐dimethylhexadecylimidazolium‐montmorillonite (IMD‐MMT) and dodecyltriphenyl phosphonium‐MMT (C₁₂PPh‐MMT). PTT hybrid fibers with various organoclay contents were melt‐spun at various draw ratios (DRs) to produce monofilaments. The thermomechanical properties and morphologies of the PTT hybrid fibers were characterized using differential scanning calorimetry, thermogravimetric analysis, wide‐angle X‐ray diffraction, electron microscopy, and mechanical tensile properties analysis. The nanostructure of the hybrid fibers was observed by both scanning and transmission electron microscopy, which showed that the clay layers were well dispersed into the matrix polymer, although some clusters or agglomerated particles were also detected. Unlike the hybrids containing IMD‐MMT, the clay layers of the C₁₂PPh‐MMT hybrid fiber were more dispersed into the matrix polymer. The thermal stability and tensile properties of the hybrid fibers increased with increasing clay content for DR = 1. However, as DR increased from 1 to 9 the ultimate strength and initial modulus of the hybrid fibers with IMD‐MMT increased slightly whereas those of C₁₂PPh‐MMT hybrid fibers decreased slightly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4535–4545, 2006     

Τhe effect of wood‐fiber type on the thermomechanical performance of a biodegradable polymer matrix

The effect of type and content of wood fibers on the thermal, mechanical and rheological behavior of the commercial biodegradable polyester product, Ecovio® (BASF) is analytically studied. Ecovio® is basically a blend of poly(butylene adipate‐terephthalate) copolyester (Ecoflex®, BASF) and polylactide. Three different types of wood fibers, based either on raw cellulose (Arbocel) or selected conifers (Lignocel), with varying fiber size at various weight fractions were used for this purpose. The role of these fibers on the thermomechanical performance of Ecovio® was investigated in terms of several experimental techniques including scanning electron microscopy, differential scanning calorimetry, dynamic mechanical analysis, creep, tensile testing, and water uptake at room temperature. At the low wood fiber content (20 wt %), Lignocel composite's properties are predominant compared with the Arbocel composites. It has been found, that at this wood content, an efficient compatibility between matrix and fibers is achieved, leading to superior reinforcement. This trend is completely reversed at higher filler loading, probably due to the poor interfacial adhesion between the matrix and Lignocel occurring at 30 wt %. This behavior was supported by all the experimental methods employed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42185.