Use of grafted aspen fibers in thermoplastic composites: IV. Effect of extreme conditions on mechanical properties of polyethylene composites

Hardwood fibers of aspen in the form of chemithermo-mechanical pulp (CTMP) have been used as reinforcement in linear low density polyethylene (LLDPE). The effect of composite treatment (immersion in boiling water, heat exposure at 105°C for seven days or at a temperature of −40°C) on resulting mechanical properties were evaluated. The grafted aspen CTMP composites showed by far the best results with regard to secant modulus, tensile strength, energy, and strain when compared to those of wood flour, mica or glass–fiber filled LLDPE, as well as to virgin LLDPE. Finally, the dimensional stability of CTMP aspen-filled LLDPE composites immersed for four hours in boiling water was better than that of mica or glass–fiber filled LLDPE.     

Surface characterization of weathered and heat‐treated wood‐based composites reinforced by styrene maleic anhydride

The aim of this study was to investigate the effect of heat‐treated lignocellulosic filler on the surface characteristics and decay resistance of the wood flour/styrene maleic anhydride (SMA) composites. In this study, heat treatment was conducted at 212°C for 8 hours. Test specimens were prepared by injection molding at 220°C. Weathering tests were performed by cycles of UV‐light irradiation for 8 hours, water spray for 15 minutes, and then conditioning for 3.45 hours in an accelerated weathering test cycle chamber. Heat‐treated wood flour/SMA composites were evaluated for color changes, and attenuated total reflectance Fourier transform infrared (FTIR) spectroscopy was used to analyze chemical changes on the sample surfaces. The wood decay tests were performed of white rot fungus, Trametes versicolor (L.: Fr.) Pilat was based on mini‐block specimens on 48% malt extract agar in petri dishes. The study showed that color changes occurred when heat‐treated filler rate is increased in this material. Therefore, materials in 10% filler rate show lower color changes than other variation. As a result of the FTIR analysis, the addition of wood filler into the SMA causes changes in the chemical structure. In addition, the increase in wood filler reduced the resistance to weathering. Decay results showed that thermally modified wood has lower mass loss caused by fungal attack than untreated wood material. The weight loss decreases with the increase in wood flour rate expect 10%T and 10%UT in all composites.     

Durability of wood flour‐plastic composites exposed to accelerated freeze–thaw cycling. II. High density polyethylene matrix

This study examined the durability of extruded HDPE/wood‐flour composites exposed to 15 accelerated cycles of water submersion, freezing, and thawing, according to ASTM standard D6662. The durability of both maple and pine composites was assessed by testing the flexural properties and density. Mercury intrusion porosimetry and scanning electron microscopy were also used to evaluate the interfacial adhesion between the matrix and wood flour before and after exposure to accelerated freeze–thaw cycling. Freeze–thaw actions had no apparent effect on the density of the composites after exposure, regardless of the wood species. However, these actions led to moisture uptake, which decreased the interfacial adhesion and increased the pore size and quantity in the composites, which resulted in a significant loss in flexural properties. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 100: 35–39, 2006     

Durability of wood flour‐plastic composites exposed to accelerated freeze–thaw cycling. Part I. Rigid PVC matrix

This study examined the effects of accelerated freeze–thaw actions on the durability of wood fiber‐plastic composites. Rigid PVC formulations filled with various concentrations of wood flour (both pine and maple) were processed in a counterrotating twin‐screw extruder and exposed to cyclic freeze–thaw actions according to ASTM Standard D6662. Freeze–thaw cycling was also modified by omitting portions of the test (either the water or freezing) to verify whether or not moisture was the primary cause for property loss. The durability of exposed samples was assessed in terms of flexural properties, density, and dimensional stability. Scanning electron micrographs of unexposed and freeze–thaw‐exposed samples were taken to qualitatively evaluate the interfacial adhesion between the wood flour and PVC matrix. The experimental results indicated that the density was not affected by freeze–thaw cycling. The dimensional stability was also relatively unaffected, although greater wood flour content exhibited greater dimensional change. The loss in stiffness of the composites was statistically significant after only two freeze–thaw cycles, regardless of both the wood species and content. Conversely, the strength of the composites was not significantly affected by five freeze–thaw cycles at lower wood flour contents (50 and 75 phr). The deleterious effects of the freeze–thaw actions on the strength of the composites became apparent at higher wood flour content (100 phr) after only two freeze–thaw cycles for maple flour and five freeze–thaw cycles for pine flour. The property loss was attributed primarily to the water portion of the cycling, which appears to have led to the decreased interfacial adhesion between the wood flour and the rigid PVC matrix. J. VINYL. ADDIT. TECHNOL. 11:1–8, 2005. © 2005 Society of Plastics Engineers.     

Effect of compatibilizer on the natural durability of wood flour/high density polyethylene composites against rainbow fungus (Coriolus versicolor)

To evaluate the effect of compatibilizer on the natural durability of wood flour/high density polyethylene composites against Coriolus versicolor, composites containing 25% and 50% by weight maple wood flour and 1% and 2% compatibilizer (Maleic anhydride polyethylene (MAPE)), respectively, were sampled. Identical specimens of the same composites without the compatibilizer were also prepared. Physical and mechanical properties of all specimens, including water absorption, flexural modulus, flexural strength, impact strength and hardness, were determined prior to and after incubation with the fungus for 14 weeks at 25°C and 75% relative humidity. Weight losses of the specimens were also determined after incubation. Results indicated that the compatibilizer had significant effects on the natural durability of the studied composite formulations so that all mechanical properties were affected by the fungus to greater extents in the case of uncompatibilized specimens than the compatibilized ones. Weight loss of the uncompatibilized composites was also higher than that of compatibilized ones. Higher water absorption was observed in all cases after incubation. However, the increase in water absorption was considerably higher in the case of uncompatibilized specimens. POLYM. COMPOS., 28:273–277, 2007. © 2007 Society of Plastics Engineers     

Rheological properties of teak wood flour reinforced HDPE and maize starch composites

Teak wood flour reinforced high density polyethylene and maize starch composites were prepared by using maleic anhydride grafted polyethylene as a compatibilizer. The mechanical properties (tensile and flexural) of all the composites increased after addition of 10%–40% teak wood flour into HDPE matrix. The complex viscosity (η*) was higher for all the composites at the low frequency, but decreased with increasing frequencies indicating a shear thinning behavior of the composites. The storage modulus and loss modulus increased for the composites compared to the HDPE at low frequencies. Damping factor peak of HDPE and composites showed high below 1 Hz, but the peak start decreasing with increasing above 1 Hz. The relaxation behavior of HDPE and the composites after incorporating teak wood flour, maize starch, and compatibilizer was obtained by Han plot. Biodegradability was enhanced with the incorporation of teak wood flour, maize starch into the composites. Appreciable water uptake and the thickness swelling for the composites indicating it's potential for interior, automobile and packaging applications.     

Effects of copper amine treatment on mechanical properties of PVC/wood‐flour composites

Copper amine–treated wood flour was added to PVC [poly(vinyl chloride)] matrix in order to manufacture PVC/wood‐flour composites. Effects of copper treatments on the mechanical properties of PVC‐wood composites were evaluated. Unnotched impact strength, flexural strength, and flexural toughness of the composites were significantly improved by the wood‐flour copper treatment. The optimum copper concentration range was 0.2 to 0.6 wt% of wood flour. Fractured surfaces were examined by using scanning electron microscopy (SEM) combined with energy‐dispersive spectroscopy (EDS). PVC/wood interfacial debonding was the main fracture mode of untreated wood‐flour composites, whereas wood‐particle pullout and breakage dominating the fractured surfaces of copper‐treated wood‐flour composites. On the fractured surfaces, more PVC could be found on the exposed copper‐treated wood particles than on untreated wood, a result suggesting improved PVC‐wood interfacial adhesion after copper treatments. J. Vinyl Addit. Technol. 10:70–78, 2004. © 2004 Society of Plastics Engineers.     

Comparative study on the effect of manchurian ash and larch wood flour on mechanical property,morphology, and rheology of HDPE/wood flour composites

Effects of wood flour species and polyethylene grafted with maleic anhydride (MA‐PE) on mechanical properties and morphology and torque rheology of high density polyethylene (HDPE)/wood flour composites have been comparatively investigated. The results demonstrated that without compatbilizer, wood flour species exhibited little influence on mechanical properties. In the presence of MA‐PE, the mechanical properties were obviously increased. On the basis of the mechanical property data obtained from wood flour extracted by different methods, the extractant was an important factor affecting the mechanical properties. Manchurian ash and larch wood flours extracted by hot water presented almost the same mechanical properties, and larch wood flour was the most beneficial to enhance the mechanical properties. The scanning electron microscopy (SEM) and the atomic force microscopy (AFM) further confirmed that interfacial adhesion and dispersion of manchurian ash wood flour in composites were effectively improved by MA‐PE. The torque results demonstrated that the chemical reactions of maleic anhydride groups on MA‐PE with hydroxyl on cellulose in wood flour probably took place due to the increase of the equilibrium torque and the appearance of the torque peak, and larch wood flour was more beneficial to prepare the composites containing the higher wood flour content. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Processability,morphology and mechanical properties of wood flour reinforced high density polyethylene composites

Abstract

Wood flour reinforced high density polyethylene (HDPE) composites have been prepared and their rheological properties measured. The melt viscosity decreased as the processing temperature increased and the wood flour content decreased. A power law model was used to describe the pseudoplasticity of these melts. Adding wood flour to HDPE produced an increase in tensile strength and modulus. Composites compounded in a twin screw extruder and treated with a coupling agent (vinyltrimethoxysilane) or a compatibliser (HDPE grafted with maleic anhydride) exhibited better mechanical properties than the corresponding unmodified composites because of improved dispersion and good adhesion between the wood fibre and the polyalkene matrix. Scanning electron microscopy of the fracture surfaces of these composites showed that both the coupling agent and compatibiliser gave superior interfacial strength between the wood fibre and the polyalkene matrix.     

Monofunctional compatibilizer with long alkyl end for fabrication of superior tensile wood flour‐polyolefin composites

A novel monofunctional compatibilizer (OID) was prepared and used as compatibilizer for fabrication of wood‐plastic composites. OID was successfully synthesized by esterification reaction of isophorone diisocyanate and octadecanol as confirmed by Fourier transform‐infrared spectra. After OID modification, the hydrophobicity of wood flour surface was enhanced as indicated by the increase of surface water contact angle. By using OID as compatibilizer, an obvious enhancement of the interfacial adhesion between wood flour and polyolefin was observed by scanning electron microscopy. As a result, the tensile properties of the obtained polypropylene/wood flour composites and polyethylene/wood flour composites were significantly enhanced. Besides, the processability of polyolefin/wood flour composites was also improved by adding OID. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44429.     

Incorporation effect of enzymatic hydrolysis lignin on the mechanical and rheological properties of the resulting wood flour/high‐density polyethylene composites

Enzymatic hydrolysis lignin (EHL) from ethanol production was used as an additive to incorporate in the wood flour/high‐density polyethylene (HDPE) composite during the melt extrusion, and the incorporating effects on the mechanical and rheological properties of the resulting composites were investigated. The addition of EHL caused an improvement in both the tensile strength and impact strength, and a reduction in the complex viscosity of the composites as evidenced by the rotational rheometry, which suggests an increased flowability of the composite melt due to incorporation of EHL. The water absorption and swelling of the composites decreased with increasing EHL content during water immersion test. The scanning electron microscopy micrographs of EHL incorporated wood flour/high‐density polyethylene composites showed a homogeneous dispersion of wood flour and EHL in the HDPE matrix. POLYM. COMPOS., 37:379–384, 2016. © 2014 Society of Plastics Engineers     

Effect of weathering cycle and manufacturing method on performance of wood flour and high‐density polyethylene composites

Wood–plastic lumber is promoted as a low‐maintenance high‐durability product. When exposed to accelerated weathering, however, wood–plastic composites may experience a color change and loss in mechanical properties. Differences in weathering cycle and composite surface characteristics can affect the rate and amount of change caused by weathering. In this study, 50% wood flour filled high‐density polyethylene composite samples were injection molded, extruded, or extruded and then planed to remove the manufacturing surface characteristics. Composites were exposed to two accelerated weathering cycles in a xenon arc weathering apparatus. This apparatus exposed the samples to xenon arc radiation, which is a combination of UV, visible, and IR radiation that is similar to solar radiation. Composites were exposed to radiation with or without water spray. After exposure to radiation and water spray, composites with more wood component at the surface (i.e., planed samples) experienced a larger percentage of total loss in flexural modulus of elasticity and strength after weathering compared with the other composites. Composites exposed to radiation only did not experience as much change in properties as those exposed to radiation with water spray. The results of this study demonstrate that exposing wood–plastic composites to water spray in combination with radiation is more severe than exposing wood–plastic composites to radiation only. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3131–3140, 2006     

Long‐term water uptake behavior of lignocellulosic‐high density polyethylene composites

Composites of different lignocellulosic materials and high‐density polyethylene were prepared and their long‐term water absorption behaviors were studied. Wood flour, rice hulls, newsprint fibers, and kenaf fibers were mixed with the polymer at 25 and 50 wt % fiber contents and 1 and 2% compatibilizer, respectively. Water absorption tests were carried out on injection‐molded specimens at room temperature for five weeks. Results indicated a significant difference among different natural fibers with kenaf fibers and newsprint fibers exhibiting the highest and wood flour and rice hulls the lowest water absorption values, respectively. Very little difference was observed between kenaf fiber and newsprint composites and between rice hulls and wood flour composites regarding their water uptake behavior. The difference between 25 and 50% fiber contents for all composite formulations increased at longer immersion times, especially for the composites with higher water absorption. Kenaf fiber composites containing 50% kenaf fibers exhibited the highest water diffusion coefficient. A strong correlation was found between the water absorption and holocellulose content of the composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3907–3911, 2006     

Ultraviolet weathering of photostabilized wood‐flour‐filled high‐density polyethylene composites

Wood‐plastic composites are being increasingly examined for nonstructural or semistructural building applications. As outdoor applications become more widespread, durability becomes an issue. Ultraviolet exposure can lead to photodegradation, which results in a change in appearance and/or mechanical properties. Photodegradation can be slowed through the addition of photostabilizers. In this study, we examined the performance of wood flour/high‐density polyethylene composites after accelerated weathering. Two 2⁴ factorial experimental designs were used to determine the effects of two hindered amine light stabilizers, an ultraviolet absorber, a colorant, and their interactions on the photostabilization of high‐density polyethyl‐ ene blends and wood flour/high‐density polyethylene composites. Color change and flexural properties were determined after 250, 500, 1000, and 2000 h of accelerated weathering. The results indicate that both the colorant and ultraviolet absorber were more effective photostabilizers for wood flour/high‐density polyethylene composites than the hindered amine light stabilizers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2609–2617, 2003     

Potassium methyl siliconate‐treated pulp fibers and their effects on wood plastic composites: Water sorption and dimensional stability

Potassium methyl siliconate (PMS) was investigated as a new nano modifier of wood fiber and wood flour to improve the compatibility between the fiber/flour and the plastic matrix in fiber reinforced plastic composites. Before injection molding, bleached and brown pulp fibers and mixed species wood flour were pretreated in PMS solutions. The morphology of the treated and untreated fiber and flour, the compatibility of PMS‐treated fiber and flour with polyethylene (PE), and the water sorption and volumetric swell of PMS‐treated fiber/flour plastic composites in a long‐term soaking test were evaluated. Fiber and flour treated with PMS increased the compatibility between the fiber/flour and the PE matrix. The increased compatibility of PMS‐treated fiber and flour with the matrix contributed to the reduction of water sorption and, thus, increased dimensional stability. For all composites, water sorption and volumetric swell of fiber/four plastic composites decreased as the ratio of fiber to flour increased. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

甲基化木粉与PE-g-MAH对木粉/HDPE复合材料力学性能的协同作用研究

主要研究了木粉表面甲基化改性和增容剂马来酸酐接枝聚乙烯(PE-g-MAH)对木粉/高密度聚乙烯(HDPE)复合材料力学性能的协同作用。木粉经表面甲基化处理后,与10%PE-g-MAH协同使用,甲基化木粉/PE-g-MAH/HDPE复合材料的拉伸强度、弯曲强度和冲击强度均明显高于未改性木粉/PE-g-MAH/HDPE复合材料,其原因在于在PE-g-MAH的作用下,甲基化木粉在聚合物基体中分布更加均匀,两者的界面作用力更高,即甲基化木粉和PE-g-MAH对提升木粉/HDPE复合材料的力学性能具有良好的协同作用。     

Effect of compatibilizers on water absorption kinetics of polypropylene/wood flour foamed composites

Polypropylene (PP)/wood flour foamed composites were prepared by taking PP:wood flour in the ratios of 100 : 0, 90 : 10, 80 : 20, 70 : 30, and 60 : 40 (w/w), with and without compatibilizers like maleic anhydride‐treated wood flour and maleic anhydride‐grafted PP (PPgMA). The foamed composite samples were employed for water swelling at 27°C, 70°C, and in steam. The absorption of water increased with increase in filler contents for all three‐temperature conditions. The maleic anhydride‐treated wood flour and PPgMA showed reduction in water swelling, and the best one was in case of the PPgMA‐foamed composites for respective conditions. Diffusion, sorption, and permeation coefficients were determined to study the absorption kinetics. FTIR spectra were also recorded for 30 wt % of filler loading for all the composites, which showed the effect of compatibilizers on reduction in water absorption in foamed PP/wood flour composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2530–2537, 2006     

Effects of repetitive processing,wood content,and coupling agent on the mechanical,thermal, and water absorption properties of wood/polypropylene green composites

In an effort to determine to what extent natural fiber/plastic composites were recyclable, this study conducted repetitive processing cycles on wood flour/polypropylene composites through extrusion up to three times followed by injection molding. Mechanical properties of the composites, containing 10–50?wt% wood flour and with/without addition of 3?wt% maleic anhydride polypropylene (MAPP) as coupling agent, were evaluated by conducting tensile test, thermal analysis, and water absorption test. Repetitive processing as well as wood content and coupling agent addition influenced physical properties of the composites. MAPP functioned well in improving fiber-matrix adhesion in terms of mechanical properties. Repetitive processing did not deteriorate the composite’s properties; rather opposite effect was shown. Thermal analysis indicated that the alteration in properties was contributed by the molecular condition of the polypropylene matrix. Water absorption increased with the wood flour content but reduced when MAPP was added and with more processing cycles.     

Enhanced thermal stability and flame retarding properties of recycled polyethylene based wood composites via addition of polyethylene/nanoclay masterbatch

Abstract

Barrier and mechanical properties of wood powder composites based on recycled polyethylene (RPE) were modified using a commercial nanoclay masterbatch. X-ray diffraction, dynamic rheology and thermogravimetric analysis measurements showed that nanoclay from the selected masterbatch was well dispersed and formed a percolation network in both virgin and RPEs. The resulting nanocomposites promoted the thermal stability of matrix significantly. Modification efficiency of nanoclay, however, was evidently influenced by the type of matrix, where the strongest effect was achieved in a low viscosity virgin high density PE. The masterbatch was incorporated into an industrial formula designed extrusion quality RPE/wood flour composite. Processing procedures, mainly compounding cycles, and material composition, mainly clay content and type of coupling agent, were optimised. Two extrusion cycles led to higher uniformity of resulting composites than one cycle. Addition of a coupling agent, which has medium viscosity and plenty functional groups, led to enhanced tensile strength. The twice compounded composites were well stiffened and strengthened via combination of 6 wt-% clay and medium viscosity coupling agent. All composites without the addition of nanoclay burned faster after ignition and dripped much earlier and more compared to the composites containing nanoclay even with as small amount as 3 wt-% and being compounded once. The material with 6 wt-% clay showed the best sample integrity and burned slowest of all the tested composites. Furthermore, no dripping during combustion was seen for this material. This study shows that the incorporation of nanoclay using the selected masterbatch can effectively improve the flame retarding properties of RPE based wood composites.     

Mold susceptibility of rigid PVC/wood‐flour composites

Rigid PVC/wood‐flour composite lumber containing either hardwood (maple) or a softwood (southern pine) wood flour at different levels of wood‐flour content was evaluated for susceptibility to fungal colonization and discoloration by using standard tests that mimicked exterior (ASTM G21) and interior (ASTM D3273) environments, respectively. In the exterior test protocol, although both types of PVC/wood‐flour composite lumber exhibited fungal colonization and discoloration, the composites containing maple exhibited greater discoloration than those containing pine. Irrespective of wood species, fungal colonization and discoloration in the composite lumber were greater at the bottom faces where they were in constant contact with moisture. The wood content range (50–100 phr) used in this study showed no effect on extent of fungal colonization and discoloration. All composites showed no discoloration in the interior test protocol. Both optical microscopy and environmental scanning electron microscopy clearly demonstrated that wood flour particulates are not completely encapsulated by the PVC matrix, so that exposed wood flour in the surface crevices of the composite lumber may serve as points of moisture sorption and staging points for fungal colonization and discoloration. J. Vinyl Addit. Technol. 10:179–186, 2004. © 2004 Society of Plastics Engineers.