Wood Flour Polypropylene Composites Research Articles

Morphology, dimensional stability and mechanical properties of polypropylene–wood flour composites with and without nanoclay

Several composites based on recycled—virgin polypropylene, wood flour and organically modified montmorillonite (commonly called ‘nanoclay’) were prepared by melt compounding. This paper aims to evaluate the potential for the use of recycled polypropylene and underutilized wood flour as material for the development of wood–plastic composites, as well as reinforcement effect of organically modified montmorillonite on them. In order to improve the poor interfacial interaction between the hydrophilic wood flour and hydrophobic polypropylene matrix, as well as polypropylene–organically modified montmorillonite, maleic anhydride-grafted polypropylene was used as a compatibilizer. Some mechanical and physical properties were evaluated. Findings of this work show that both recycled and virgin polypropylene can be used in manufacture of wood–plastic composites and there is no significant difference in the properties of resulting nanocomposites. It was found that mechanical properties of polypropylene containing 40wt% wood flour reinforcement remain essentially unchanged when the virgin polypropylene in the matrix is replaced be recycled polypropylene. Morphologies of the nanocomposites were analyzed by scanning electron microscopy and X-ray diffraction, and the results showed increased d-spacing of clay layers indicating enhanced compatibility between polypropylene and clay and wood flour. Consequently, polypropylene recycled from postconsumer applications can be used in high-value nanocomposites without going the expense of separating out impurities from the polymer.

Impact strength improvement of wood flour–recycled polypropylene composites

AbstractIn this research, the improvement of the impact strength of wood flour–recycled polypropylene (PP) composites through impact modification was studied. For this purpose, a virgin polypropylene (VPP) was thermomechanically degraded by five extrusions under controlled conditions in a twin‐screw extruder at a rotor speed of 100 rpm and a temperature of 190°C. PP (VPP and recycled PP at the second and fifth stages) and wood flour were compounded at 50 wt % wood flour loading in a counterrotating twin‐screw extruder in the presence different contents of ethylene vinyl acetate (EVA) to produce the wood flour–PP composites. From the results, the composites containing recycled PP exhibited significantly lower impact strengths. The addition of EVA up to 9 wt % increased the impact strengths of the composites made with PP recycled two and five times by about 63 and 41%, respectively. The composites containing VPP exhibited higher impact strengths than those containing recycled PP and EVA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The influence of wood flour and compatibilizer (m-TMI-g-PP) on crystallization and melting behavior of polypropylene

Abstract Wood flour/polypropylene composites (WPC) were prepared by melt extruding with different wood flour (WF) loadings. The non-isothermal crystallization and melting was studied with different WF loadings, for W40P60 and W40P60M6, the melting was investigated after non-isothermal and isothermal crystalline. Comparing with neat polypropylene, the melting behavior of the composites, both non-isothermally and isothermally, was investigated by differential scanning calorimetry (DSC). The results showed that WF was an effective heterogeneous nucleating agent, as evidenced by an increase in the crystallization temperature and the crystallinity for melt crystallization of PP with increasing WF content. For the non-isothermal samples, the origins of the double melting behaviors were discussed, based on the DSC results of PP. The XRD measurements confirmed that no crystalline transition existed during the non-isothermal crystallization process. With m-TMI-g-PP adding, due to compatibilization phenomenon were ...

Evaluation on the effect of wood flour and coupling agent content on the hygroscopic thickness swelling rate of polypropylene composites

The effect of wood flour and coupling agent content on the hygroscopic thickness swelling rate of polypropylene composites was investigated in this study. To meet this objective, the wood flour was compounded with polypropylene and coupling agent in an internal mixer; then the samples were fabricated by injection molding. The concentration was varied from 40 to 60% for wood flour and from 0 to 4% for coupling agent. A swelling model developed by Shi and Gardner (2006) was used to study the thickness swelling process of polypropylene/wood flour composites, from which the parameter KSR can be used to quantify the swelling rate. The results indicated that the swelling model provided a good prediction of the hygroscopic thickness swelling process of polypropylene-wood flour composites immersed in water. The minimum thickness swelling values were observed in composites made of 40% wood flour and 4% of PP-g-MA. Thickness swelling of the composite increased with immersion time, reaching a certain value at saturation point, after which the composites water content remained constant. Also, a good linear relationship was fit between KSR and coupling agent contents. When the coupling agent content increased, KSR linearly decreased. The maximum tensile modulus was achieved with 60% wood flour and 4% of PP-g-MA. The SEM revealed a positive effect of coupling agent on interfacial bonding between sawdust flour and polymer matrix.

Influence of ammonium polyphosphate modified with 3‐(methylacryloxyl) propyltrimethoxy silane on mechanical and thermal properties of wood flour–polypropylene composites

AbstractIn this article, the influence of ammonium polyphosphate (APP) and ammonium polyphosphate modified with 3‐(Methylacryloxyl) propyltrimethoxy silane (M‐APP) on mechanical properties, flame retardancy, and thermal degradation of wood flour–polypropylene composites (WF/PP composites) have been investigated. Polypropylene grafted with m‐isopropenyl‐α,α‐dimethylbenzyl‐isocyanate (m‐TMI‐g‐PP) was used to improve the adhesion of WF/PP composites. APP and M‐APP were used as flame retardants. The experimental results demonstrated that addition of M‐APP obviously enhanced mechanical properties of WF/PP composites. According to cone calorimetry results, M‐APP is also an effective flame retardant for WF/PP composites, compared to that of APP. It was also found that M‐APP decreased the 1% weight loss temperature and increased char residue. The thermal degradation of wood flour based upon the first peak temperature of wood decreased from 329.3 to 322.9°C and the thermal degradation of PP based upon the second peak temperature of PP improve from 518.0 to 519.6°C, when M‐APP was added to the WF/PP composites. From SEM results the char layer of the 25% M‐APP systems is much more intumescent than that of the 25% APP systems, indicating that 3‐(Methylacryloxyl) propyltrimethoxy silane can improve the char‐forming ability of WF/PP composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Effect of oxidized polypropylene as a new compatibilizer on the water absorption and mechanical properties of wood flour–polypropylene composites

AbstractThe effect of oxidized polypropylene (OPP) as new compatibilizer on the water absorption and mechanical properties of wood flour–polypropylene (PP) composites were studied and compared with maleic anhydride grafted polypropylene (MAPP). The oxidation of PP was performed in the molten state in the presence of air. Wood flour, PP, and the compatibilizers (OPP and MAPP) were mixed in an internal mixer at temperature of 190°C. The amorphous composites removed from the mixer were then pressed into plates that had a nominal thickness of 2 mm and nominal dimensions of 15 × 15 cm2 with a laboratory hydraulic hot press at 190°C. Physical and mechanical tests showed that the wood flour–PP composites with OPP exhibited higher flexural and impact properties but lower water absorption than MAPP. All of the composites with 2% compatibilizers (OPP and MAPP) gave higher flexural and impact properties and lower water absorption compared to those with 4% compatibilizers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Effect of Thermo-Mechanical Degradation of Polypropylene on Hygroscopic Characteristics of Wood Flour-Polypropylene Composites

In this research, the influence of thermo-mechanical degradation of polypropylene (PP) on water absorption and thickness swelling of beech wood flour–PP composites were studied. For this purpose, a virgin PP was thermo-mechanically degraded by two times extrusion under controlled conditions. The results showed that the melt flow index, water absorption and thickness swelling of PP significantly increase by extrusion and re-extrusion. The virgin PP and degraded polypropylene were compounded with wood flour (at 60% by weight wood flour loading) in a counter-rotating twin-screw extruder in presence or absence of MAPP to produce wood flour–PP composites. From the results, the composites containing recycled PP exhibited higher water absorption and thickness swelling. The use of MAPP decreased water absorption and thickness swelling in composites made of virgin or recycled PP.

Rheological, Mechanical and Thermal Behaviour of Wood Polymer Composites Based on Recycled Polypropylene

The aim of this paper was to investigate the effect of recycled polypropylene (PP) on the rheological, mechanical and thermal properties of wood flour polypropylene composites. Beforehand, the influence of wood flour treated with a coupling agent on the rheological behaviour had been looked at. By analysing moduli and viscosity curves and studying the thermal and mechanical properties of samples with 10% filler it was possible to see that the recycled PP that was added change in either its physical properties or its rheology. In the other wood plastic composites (WPC) studied, slight changes in the rheology behaviour were observed. However, the same processing parameters may be used with and without recycled PP. Recycled PP is appropriate for these kinds of composites to maintain the optimal rheological properties that make it easier to process the material by extrusion. Furthermore, it is also possible to maintain the thermal and mechanical properties in comparison with the behaviour of virgin PP/wood flour composites.

Preliminary study of viscoelastic properties of MAPP-modified wood flour/polypropylene composites

Viscoelastic properties of maleated polypropylene (MAPP)-modified wood flour/polypropylene composites (WPC) were investigated by both a compression stress relaxation method and dynamic mechanical analyses (DMA). Three wood to polymer ratios (40:60, 60:40, and 80:20) and five MAPP loading levels (0, 1, 2, 4 and 8%) were used to study their effects on the viscoelastic properties of MAPP-WPC. The results show that: 1) higher wood to polymer ratio corresponds to higher stress relaxation levels for unmodified WPC. The modification with MAPP has an obvious effect on the stress relaxation of MAPP-WPC at higher wood to polymer ratios (60:40 and 80:20), but almost no effect at the 40:60 wood to polymer ratio. The optimal MAPP loading level for the wood to polymer ratio of 60:40 appears at 1%; 2) the storage modulus reaches its maximum at a MAPP loading level of 1% for wood to polymer ratios of 40:60 and 60:40, while for the 80:20 wood to polymer ratio, a higher storage modulus is observed at higher MAPP loading levels, which is quite consistent with the stress relaxation results. The results suggested that a suitable loading level of MAPP has a positive effect on the viscoelastic properties of WPC at higher wood to polymer ratios. Excessive MAPP loading would have resulted in adverse effects.

Effects of vinyltrimethoxy silane on mechanical properties and morphology of polypropylene‐woodflour composites

AbstractThe effects of composition and interface modification on the tensile properties and the impact resistance of different woodflour/polypropylene composites (WPC) were studied. The woodflour was treated with vinyltrimethoxy silane as a coupling agent, and its effect on the WPC properties was examined. In addition, the tensile data were fitted with several semiempirical models to clarify the mechanical behavior of the composites. The Pukánszky parameters obtained from the fit of the tensile strength data revealed that the distribution of the filler was more homogeneous in the composites containing silane and that interaction between components was improved. The impact strength was maximal for the composites containing 30% of silane‐treated woodflour. Morphological analysis by SEM revealed that the woodflour tended to form agglomerates when present in relatively high amounts in the formulations. For the silane‐treated composites, the dispersion of the filler into the polypropylene (PP) matrix improved, although surface treatment blocked the inclusion of PP into the wood cells. This probably decreased the elastic moduli, even when the filler‐matrix interaction was improved. The beneficial effects of the coupling agent on the WPC properties were greater in the materials containing a relatively low amount of filler (up to 30%); the effectiveness of 0.5% and 1% organosilane were very similar, demonstrating the effectiveness of the coupling agent. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers

Design of new polypropylene–woodflour composites: Processing and physical characterization

AbstractWoodflour/polypropylene composites were prepared with 10 and 20% in weight of woodflour (WF). The influence of the WF, the compatibilizer, and processing aid (WP) in the crystalline structure of the polypropylene was studied by thermal analysis. The results showed that the WF acts as a nucleating agent, increasing the crystallization rate of the PP at the cooling rates studied. The morphological study by SEM proved that the WP increased the dispersion of the filler into the PP matrix, and the ionomer, used like compatibilized improved the adhesion between the PP and the filler obtaining a more uniform morphology. The mechanical properties indicated that the incorporation of the ionomer and the WP enhanced the ductility of the composites at the same time that the materials reached a more uniform morphology. The amount of additives (compatibilizer and WP) included in the woodflour‐plastic composite (WPC) formulations was small, for this, the formulations are suitable to use in a possible industrial application. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

Analysis of the isothermal crystallization of polypropylene/wood flour composites

Isothermal crystallization and melting of isotactic polypropylene in binary polypropylene-wood flour composites has been studied by DSC, and the influence of an ethylene-methacrylic acid copolymer interfacial agent analyzed. Wood flour induces a slight nucleating effect, reducing the basal interfacial free energy of nucleation and increasing the overall crystallization rate. The interfacial agent generates a compatibilization phenomenon and an increase in the basal interfacial free energies with respect to the binary composites. In both binary and ternary systems the melting behaviour is a function of undercooling and is unaltered by the presence of either wood flour or the interfacial agent.

Effect of Re-Compounding on the Properties of Polypropylene / Wood Flour Composites

Two different mixers were used for re-compounding of wood flour / polypropylene composites (WPC): internal Banbury mixer and co-rotating twin-screw extruder. Five cycles in an internal mixer and twelve cycles in an extruder were performed on WPC in order to compare the properties of composites. After 3 cycles in an internal mixer, an increase of the WPC mechanical properties (tensile, flexural and impact strength) and a decrease of water uptake was observed. Further increase of the number of cycles in an internal mixer leads to a significant decrease of WPC properties, as long as the properties remain unchanged, if reprocessing was done in extruder. More significant degradation of WPC occurred in an internal mixer compared to the extruder, therefore only 10% of the recyclate prepared in the Banbury mixer and 30% of the recyclate prepared in the extruder can be added to virgin WPC without a decrease of its properties.

Effects of vinyltrimethoxy silane on thermal properties and dynamic mechanical properties of polypropylene–wood flour composites

AbstractThe viability of vinyltrimethoxy silane was investigated as a coupling agent for the manufacture of wood–plastic composites (WPC). The effect of silane pretreatment of the wood flour on the thermal and the dynamic mechanical properties and thermal degradation properties of the composites were studied. Moreover, the effect of organosilane on the properties of composites was compared with the effect of maleated polypropylene (MAPP). DSC studies indicated that the wood flour acts as a PP‐nucleating agent, increasing the PP crystallization rate. In general, pretreatment with small amounts of silane improved this behavior in all the WPCs studied. Thermal degradation studies of the WPCs indicated that the presence of wood flour delayed degradation of the PP. Silane pretreatment of the wood flour augmented this effect, though without significantly affecting cellulose degradation. Studies of dynamic mechanical properties revealed that the wood flour (at up to 30 wt %) increased storage modulus values with respect to those of pure PP; in WPCs with a higher wood flour amount, there was no additional increase in storage modulus. Pretreatment of the wood flour with silane basically had no effect on the dynamic mechanical properties of the WPC. These results show that with small amounts of vinyltrimethoxy silane similar properties to the MAPP are reached. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The effect of epoxy‐polyester hybrid resin on mechanical properties, rheological behavior, and water absorption of polypropylene wood flour composites

AbstractThe effect of epoxy resin on mechanical and Rheological properties, and moisture absorption of wood flour polypropylene composites (WPCs) were investigated. The reactive mixing of epoxy resin with 30, and 40 wt% wood flour and polypropylene (PP) was carried out in twin screw extruder with a special screw elements arrangement. PP grafted maleic anhydrides (MPP) were used as coupling agent to improve the interfacial interactions of wood flour, epoxy resin, and PP. The tensile strength of composites decreased, and elastic modulus and moisture absorption increased with increasing epoxy resin content. The complex viscosity η* increased with increasing epoxy resin content of composites, and a synergistic effect in increasing the η* was observed at 3 wt% resin. The epoxy resin modified wood‐PP composites that chemically coupled by MPP showed minimum water absorption with highest elastic modulus. The experimental oscillation rheologyical data were used to drive a model to predict the flow behavior of WPCs, in a wide range of frequencies. POLYM. ENG. SCI., 47:2041–2048, 2007. © 2007 Society of Plastics Engineers

Surface deterioration of wood-flour polypropylene composites by weathering trials

The market for wood-fiber plastic composites (WPCs) is expanding rapidly in many countries including Japan, where WPCs are mainly used for exterior products. In such applications, WPCs undergo undesirable color change, chalking, and shrinkage and swelling, and accordingly there is a need to better understand the mechanisms responsible for the weathering of WPC and develop methods of improving their weathering resistance. In this study, weatherability of WPC was assessed by natural and accelerated weathering trials. Discoloration (whitening) of WPC during exposure was caused by degradation of both wood and plastic. Darker color pigments as additives improved the color stability of WPC; however, chalking on the surfaces still occurred. The color stability of WPC was improved by application of exterior coatings. Preweathering of WPC (before coatings were applied) increased the absorption of coatings by the WPC and had a positive effect on the color stability and prevented chalking of the composites.

Improving the properties of polypropylene–wood flour composites by utilization of maleated adhesion promoters

Polymer composites filled with natural organic fillers have gained a significant interest during the last few years, because of several advantages they can offer compared with properties of inorganic-mineral fillers. However, these composites (based, in most cases, on polyolefins) often show a reduction in some mechanical properties. This is mainly due to the problems regarding dispersion of the polar filler particles in the non-polar polymer matrix and their interfacial adhesion with polymer chains. In this work, polypropylene–wood flour composites were prepared and the effect of the addition of a maleated polypropylene was investigated. The two materials were compounded by an industrial co-rotating twin screw extruder, with two different compositions, without and with addition of Licomont AR504® (maleic anhydride-grafted polypropylene wax). The extruded material was then compression molded, which provided the specimens for tensile and impact tests. Water uptake was measured; the morphology of the fracture surfaces of the samples coming out from mechanical tests was investigated through SEM analysis. Rheological characterization was carried out as well. The addition of the adhesion promoter allowed a decrease in water uptake; mechanical properties were improved as well, especially elastic modulus and tensile strength; impact strength increased in the case of unnotched samples, while notched ones did not show remarkable differences. SEM analysis of the fracture surfaces also showed an overall change in the morphology as a consequence of the utilization of the adhesion promoter.

Studies on the Thermal and Mechanical Properties of Foamed Wood-Polymer Composites

Wood flour-polypropylene foamed composites, in ratios of 10:90, 20:80, 30:70, and 40:60 (wt./wt.), were prepared with and without maleic anhydride treatment of wood flour and maleic anhydride-grafted PP (MAgPP). The effects of the amount of wood flour and its treatment on the morphology, the mechanical properties, and the thermal properties of the composites were investigated. Vicat softening temperatures (VST) were recorded as 112.9°C, 103.2°C, and 96.2°C for MAgPP wood flour (MPP), maleic anhydride-treated wood flour (MWF), and untreated wood flour (UWF) (40:60 wt./wt.) foamed composites, respectively. The heat distortion temperatures (HDT) were measured to be 80°C, 76°C, and 58°C for the respective composites. DSC thermograms showed an increase in the crystallinity of MPP and MWF composites with an increase in the ratio of wood flour in the composite, whereas the opposite trend was observed in untreated wood flour. Except for impact strength and flexural strength, Young's modulus, flexural modulus, and hardness all increased with an increase in wood flour content. The micrographs confirmed the foaming. The improvement in the properties of the composites is due to the increment in interfacial bonding between polymer and wood flour, which is caused by the compatibilizers.

Morphology and mechanical properties of polypropylene-wood flour composites

The microstructure and mechanical properties of polymer composites based on polypropylene and wood flour modified with monochloroacetic acid were investigated. Scanning electron microscopy and wide-angle X-ray diffraction were used as methods to probe the composite microstructures, while the tensile test was used to measure the physical strength. The wood flour modification was performed at different levels of monochloroacetic acid, ranging from 0.01 to 1 mol, while the modified wood flour was used as filler for polypropylene at 10, 20 and 30 wt.-%. It was found that increasing the monochloroacetic acid fraction influences the microstructure of the composites and leads to more homogeneous products. The introduction of non-modified wood flour decreases the polypropylene crystallization degree, but it improves after introduction of monochloroacetic acid. Physical-mechanical tests showed positive effects on tensile tests and Charpy notched impact strength. The new composites appear to be promising materials for construction purposes.

Process Rheology and Mechanical Property Correlationship of Wood Flour-Polypropylene Composites

The rheological properties of wood fiber reinforced thermoplastics blends are important to practical industry application, however few research is available regarding this field. In this study, a C. W. Brabender Plasti-Corder torque rheometer was used to examine the flow behavior of wood flour filled polypropylene (PP) composites. The effect of loading level of wood flour and an internal lubricant on the rheological properties was studied. The results show that the wood flour-PP blends behavior as pseudo-plastics or shear-thinning flow under the experimental conditions investigated. The addition of internal lubricant is effective in reducing the apparent viscosity that tends to increase with a higher loading of wood flour. The effect of shear rate on the efficiency of internal lubricant was also investigated. For practical application, it is recommended to use both internal lubricant and phase compatibilizer such as Maleic Anhydride grafted polypropylene (MAgPP), thus improving the processing operation while maintaining the strength properties of the wood flour-PP composites.