Wood Polypropylene Composites Research Articles

Characterization of fly ash reinforced wood polypropylene composites

In this study, fly ash, which is released as waste from thermal power plants and has negative effects on the environment, was evaluated as a filler in wood-plastic composite materials (WPC). For this purpose, inorganic fly ash from thermal power plants was mixed with polypropylene (PP) thermoplastic polymer at 10%, 20%, 30%, 40%, and 50% by extrusion method instead of wood flour used in wood plastic composite materials. Maleic anhydride-treated polypropylene (MAPP) was used to strengthen the bonding during WPC production. The material mixed in extrusion was passed through a crusher and turned into pellets. Test samples were prepared using injection molding of pelletized WPC material. Density, thickness swelling, water absorption, modulus of rupture, impact strength, modulus of elasticity in bending, tensile strength, janka hardness, differential scanning calorimetry (DSC), and thermogravimetric analyses (TGA) were performed on the prepared test samples. The results indicated that as the amount of fly ash used in the wood-plastic composite material increases, the density increases but the thermal degradation temperature of the material, water uptake, the swelling ratio to its thickness, tensile strength, impact strength, janka hardness, modulus of rupture, and modulus of elasticity decrease.

Polipropilen ve söğüt (Salix babylonica L.) odunu/kabuğu ile üretilen biyokompozitlerin özellikleri

The present study investigates the influence of various components of wood-plastic composites (WPCs) namely wood (W), inner bark (IB), outer bark (OB), and their varied percentage mixture on the mechanical behaviour. To achieve this goal, willow W, IB and OB flours were used as reinforcements at different weight percentages (17%, 27%, and 40%) in combination with polypropylene (PP) at varying weight percentages (44%, 58%, and 64%) along with a 2% compatibilizer. These constituents were processed in a twin-screw extruder with each treatment having a distinct mass proportion of reinforcement to polypropylene. Subsequently, test samples were fabricated using an injection molding machine from the obtained pellets. The mechanical properties of the resulting biocomposites were evaluated in accordance with ASTM standards. It was observed that, the flexural and tensile characteristics of the WPCs improved by the increasing inner bark content. Based on the findings of this investigation, a formulation comprising 27% wood, 27% inner bark, 44% polypropylene and 2% compatibilizing agent (W/IB/PP/MAPP) can be recommended where high mechanical properties are required. However, the other reinforced biocomposites exhibited notably lower notched impact strength compared to pure polypropylene.

Tribological behaviour of green wood-based unrecycled and recycled polypropylene composites

In this study we evaluated the tribological performance of polypropylene composites with wood-flour fillers obtained as a by-product from the wood-processing industry, which were based on unrecycled and recycled polypropylene polymer matrices. The mechanical properties of polypropylene-wood composites with wood-filler loadings of 0–40 wt % were determined with tensile tests and their friction and wear behaviours were studied with dry reciprocating ball-on-disc sliding tests against 100Cr6 steel balls at room temperature. The addition of the wood fillers resulted in a significant improvement in the tribological performance compared to the neat, unrecycled, and recycled polypropylene materials: the friction coefficient decreased by up to 30%, while the wear resistance was improved by up to two orders of magnitude. While neat unrecycled polymers have better properties than recycled, addition of 40 wt % wood-filler content in both, recycled and unrecycled composites, resulted in almost the same level of coefficient of friction (∼0.25) and wear coefficient (2 × 10−6 mm3/(Nm) to 3 × 10−6 mm3/(Nm)). Even with the addition of as low as 5 wt % of wood fibres the wear resistance was improved for 63% and 43% for unrecycled and recycled composites, respectively, which indicates that the use of wood fillers could be a sustainable and cost-effective way to improve the polymer tribological performance, and could compensate for the normally poorer properties of recycled materials, making the recycled polypropylene-wood composites a suitable sustainable choice for tribological applications.

Impact of Intensive Mixing and Shearing Elements on the Effectiveness of Extrusion of Wood Polypropylene Composites

Impact of Intensive Mixing and Shearing Elements on the Effectiveness of Extrusion of Wood Polypropylene Composites

Study of effect of wood-flour content on mechanical, thermal, rheological properties and thermoformability of wood-polypropylene composites

Abstract Wood plastic composites (WPC) were made from polypropylene (PP), impact copolymer (ICP) and wood flour (WF) by varying the WF content from 10 to 40% with PP grafted maleic anhydride as a coupling agent. The effect of varying WF content was studied on rheological, thermal, mechanical properties and dynamic mechanical properties. Experimental small amplitude oscillatory shear (SAOS) data was compared with the Einstein–Batchelor and empirical Krieger–Dougherty relations. Significant dependence of mechanical and rheological properties on WF content was observed. Young’s modulus, flexural modulus and dynamic shear viscosity increased with WF content. Results of dynamic mechanical analysis (DMA) showed increase in storage modulus with WF content. Three millimeter thick compression molded composites sheets were thermoformed using axisymmetric molds with two draw depths. Sag observed visually during thermoforming decreased with increasing WF content. Components made from the composites showed close to uniform thickness distribution as compared to those from ICP.

Experimental Investigation on Thermal Properties of Wood-Plastic Composites as Flat Panels

The aim of this research is investigating the thermal properties of wood-plastic composites (WPCs) in the form of flat panels. The study has included many properties such as: thermal conductivity, thermal stability, thermal expansion and melting point. The WPCs have made of high-density polyethylene (HDPE) and polypropylene (PP) incorporated with wood flour taken from pine trees. The studied concentrations of wood flour in the composites are (10, 20 or 30 %). The work was performed experimentally by manufacturing the specimens and measuring the thermal properties. The results show that the addition of 10% wood flour to the composite, leads to a reduction in the thermal conductivity of 4-10%, a reduction in thermal expansion of 8-12%, and an increase in the melting point of (2-3°C) for both HDPE and PP wood composites. It was found that wood could be used with plastics that have low melting points, such as: HDPE, LDPE, PP, PVDF and PA, to ensure high thermal stability.

Comparison of the Physico-Mechanical and Weathering Properties of Wood-Plastic Composites Made of Wood Fibers from Discarded Parts of Pomelo Trees and Polypropylene.

The purpose of this study is to compare the characteristics of wood–plastic composites (WPCs) made of polypropylene (PP) and wood fibers (WFs) from discarded stems, branches, and roots of pomelo trees. The results show that the WPCs made of 30–60 mesh WFs from stems have better physical, flexural, and tensile properties than other WPCs. However, the flexural strengths of all WPCs are not only comparable to those of commercial wood–PP composites but also meet the strength requirements of the Chinese National Standard for exterior WPCs. In addition, the color change of WPCs that contained branch WFs was lower than that of WPCs that contained stem or root WFs during the initial stage of the accelerated weathering test, but the surface color parameters of all WPCs were very similar after 500 h of xenon arc accelerated weathering. Scanning electron microscope (SEM) micrographs showed many cracks on the surfaces of WPCs after accelerated weathering for 500 h, but their flexural modulus of rupture (MOR) and modulus of elasticity (MOE) values did not differ significantly during weathering. Thus, all the discarded parts of pomelo trees can be used to manufacture WPCs, and there were no significant differences in their weathering properties during 500 h of xenon arc accelerated weathering.

Influence of wood thermal modification on the supermolecular structure of polypropylene composites

AbstractThe thermal modification of wood can be an interesting way of improving adhesion in polymer composites, although the mechanical properties of composites with heat treated wood presented so far in many works arouse much controversy. In this work, effects of thermal modification of wood on the supermolecular structure and morphology of wood/polypropylene composites (WPC) were investigated using X‐ray diffraction, hot stage optical microscopy, and differential scanning calorimetry. A significant impact of the conditions of thermal wood modification on the formation of polymorphic varieties of the polymer matrix has been demonstrated. Furthermore, thermal treatment also affected the nucleation activity of wood, which was confirmed by determined parameters such as, crystal conversion, half crystallization time, and crystallization temperature. In addition, differences in the formation of transcrystalline structures responsible for the level of interfacial adhesion were depicted based on hot stage optical microscopy. Mechanical tests have shown that obtaining the appropriate strength properties of composite materials depends on the selection of appropriate conditions for thermal modification, which determine the supermolecular structure and nucleation activity. The obtained results, not reported so far, are extremely important when designing WPC composite materials with strictly defined physicochemical parameters.

Mechanical and thermal behavior analysis of wood–polypropylene composites

Bio-based materials have attracted great attention due to their good mechanical properties, biodegradability, low cost, and easy processing, especially abundant resources. In this work, polypropylene (PP) composites reinforced with 15, 30 and 45 wt% wood powder (WP) were prepared by injection molding and their thermal, mechanical, and dynamic mechanical properties were characterized. It was found that the strength and modulus of the composite materials in the tensile and bending tests significantly increased, but the impact strength decreased. The dynamic mechanical test also showed that the storage modulus increased with the increase of WP content. WP endowed the composite material with rigidity and strength, but it was not good for toughness. Besides, the addition of WP did not change the crystal structure of the composites, while the degree of crystallinity decreased. WP-filled PP composites with stable mechanical and thermal properties have great potential to replace traditional glass fiber-reinforced composites in many fields such as construction, sports equipment, and the automotive industry.

Effect of repeated cycles of wetting and drying on mechanical properties of wood–polypropylene composites

Wood plastic composites (WPCs) are being used for many outdoor applications such as fencing, railing and decking. In outdoor conditions, composites are exposed to varying atmospheric conditions which may influence its mechanical properties. Among the various effects, most predominant one is the moisture absorption due to rainfall. It is necessary to evaluate the effect of moisture absorption/desorption on mechanical properties of WPC. In the present investigation, Melia dubia wood fibre-reinforced polypropylene composites were prepared with and without coupling agent at 40 and 60% fibre loading. Composites were also prepared with three different wood fibre sizes. The composites were exposed to 25 cycles of wetting and drying. During each cycle, the samples were immersed in water for a period of 100 h followed by drying in atmospheric condition for 100 h. Samples were weighed after wetting and drying in each cycle, and mechanical properties were evaluated at 0, 5, 10 and 25 cycles. The results indicated that the composites with higher wood content and fine particle size exhibited higher water absorption and increased loss in mechanical properties. Composites prepared with coupling agent exhibited relative lower moisture absorption and smaller loss in mechanical properties compared to uncoupled composites.

Water Absorption and Hygrothermal Aging Behavior of Wood-Polypropylene Composites.

Environmentally sound composites reinforced with natural fibers or particles interest many researchers and engineers due to their great potential to substitute the traditional composites reinforced with glass fibers. However, the sensitivity of natural fiber-reinforced composites to water has limited their applications. In this paper, wood powder-reinforced polypropylene composites (WPCs) with various wood content were prepared and subjected to water absorption tests to study the water absorption procedure and the effect of water absorbed in the specimens on the mechanical properties. Water soaking tests were carried out by immersion of composite specimens in a container of distilled water maintained at three different temperatures, 23, 60 and 80 °C. The results showed that the moisture absorption content was related to wood powder percentage and they had a positive relationship. The transfer process of water molecules in the sample was found to follow the Fickian model and the diffusion constant increased with elevated water temperature. In addition, tensile and bending tests of both dry and wet composite samples were conducted and the results indicated that water absorbed in composite specimens degraded their mechanical properties. The tensile strength and modulus of the composites reinforced with 15, 30, 45 wt % wood powder decreased by 5.79%, 17.2%, 32.06% and 25.31%, 33.6%, 47.3% respectively, compared with their corresponding dry specimens. The flexural strength and modulus of the composite samples exhibited a similar result. Furthermore, dynamic mechanical analysis (DMA) also confirmed that the detrimental effect of water molecules on the composite specimens.

Effect of wood particle size on selected properties of neat and recycled wood polypropylene composites

Neat polypropylene (PP)- and post-industrial recycled polypropylene (rPP)-based wood-plastic composites (WPC) were manufactured using 40% mahogany wood flour (WF). The effect of particle size (0.074 to 0.149 mm, 0.177 to 0.250 mm, and 0.400 to 0.841 mm) on the selected properties of PP and rPP composites was studied. The influence of 3% maleic anhydride grafted polypropylene (MAPP) presence in the formulation was also evaluated. Test specimens were manufactured using a combination of extrusion and injection molding processes. The density and mechanical properties, such as flexural strength, flexural modulus, tensile strength, tensile modulus, elongation at break, hardness and impact strength values were determined. Morphology of the manufactured composites was also studied using scanning electron microscopy (SEM) analysis. Results showed that the particle size, polypropylene type (neat or recycled), and presence of MAPP had important effects on WPC’s properties. Density, flexural modulus, tensile modulus, and impact strength values increased with decreased particle size regardless of the presence of MAPP. Flexural strength values increased with decreased particle size without MAPP. Regardless of particle size, addition of MAPP in composites provided higher flexural strength, flexural modulus, tensile strength, and tensile modulus values but lower elongation at break values compared to composites without MAPP.

High-energy multiple impact (HEMI) tests of wood–polypropylene composites: new insights in structural integrity

ABSTRACT The structural integrity of wood–polymer composites (WPC) has not been fully investigated, which can be attributed to a lack of applicable test procedures. In this study, wood–polypropylene composites were assessed by High-Energy Multiple Impact (HEMI) testing. The acquired composites were based on wood particles from various sources and different wood fibre contents, respectively. With respect to wood fibre content, a clear relationship between resistance to impact milling (RIM) and unnotched impact bending strength (a cU) was obtained. The lower the fibre content of the WPC the more structural integrity was retained. In return, various wood sources had no effect on a cU, but a major impact on RIM values. RIM is suggested to be predominantly affected by structural features, such as fibre/particle content and characteristics, particle agglomerations, and spatial void distribution.

Changes in colour and mechanical properties of wood polypropylene composites on natural weathering

This comparative study focused on understanding the effect of coupling agent and particle size on weath-ering behaviour of wood polypropylene composite. Two coupling agents, namely maleic anhydride grafted polypropylene and m-TMI (m-Isopropenyl-α,α− dimethylbenzyl isocyanate) grafted polypropylene were used in preparation of the composites. The composites were exposed to outdoor conditions for one year and changes in surface colour and mechanical properties were measured after 2, 4, 8 and 12 months of natural weathering. During the initial four months of weathering considerable colour change was observed with increase in light-ness. Mechanical properties were unaffected largely for the initial four months and thereafter started declining. Overall, tensile strength decreased by about 15 % and flexural strength decreased by about 8 % after one year of weathering. The flexural modulus also decreased by about 10 %. Wood particle size was found to affect the aesthetic and strength of the composites after natural weathering. Coupling agents had a positive impact on mechanical properties however their influence on weathering degradation was not noticeable

Effect of Temperature and Strain Rate on the Flexural Behavior of Wood-Polypropylene Composites.

The mechanical properties of wood-polypropylene composites exhibit typical viscoelasticity. However, there is little information on the mechanical properties of wood-polypropylene composites related to temperature and time, which limits the use of wood-polypropylene composites as structural components. Here, the effect of time (strain rate) and temperature on the flexural properties and the master curve of the storage modulus used to predict the long-term performance of wood-polypropylene composites were investigated. The results showed that the flexural strength and modulus increased linearly with the increase of wood contend, which can increase by 134% and 257% respectively when the mass fraction of wood powder reached 45%. Moreover, there was a positive linear relationship between flexural strength and ln strain rate, while the flexural strength and modulus decreased as temperature elevated. The storage modulus as a function of frequency (time) and temperature confirmed this trend. To evaluate the long-term performance, the storage modulus master curve was constructed and the respective activation energy was calculated, which revealed that the long-term performance of the samples depended on the matrix and the addition of an appropriate amount of wood powder was beneficial to improve their durability.

Resistance of Injection Molded Wood-Polypropylene Composites against Basidiomycetes According to EN 15534-1: New Insights on the Test Procedure, Structural Alterations, and Impact of Wood Source

In this study, we investigated injection molded wood-polypropylene composites based on various wood sources and their decay resistance against white rot (Trametes versicolor) and brown rot (Coniophora puteana) in a laboratory test according to EN 15534-1:2014. The manufactured composites consisted of poplar (Populus spp.), willow (Salix spp.), European beech (Fagus sylvatica L.), Norway spruce (Picea abies (L.) H. Karst.), and a commercial wood source (Arbocel® C100), respectively. All formulations were compounded on a co-rotating twin screw extruder and subsequently injection molded to wood–PP specimens with a wood content of 60% or 70% by weight. It was found that the test procedure had a significant effect on the mechanical properties. Loss in mechanical properties was primarily caused by moisture and less by fungal decay. Moisture caused a loss in the modulus of rupture and modulus of elasticity of 34 to 45% and 29 to 73%, respectively. Mean mass and wood mass losses were up to a maximum of 3.7% and 5.3%, respectively. The high resistance against fungal decay was generally attributed to the encapsulation of wood by the polymer matrix caused by sample preparation, and enhanced by reduced moisture uptake during the preconditioning procedure. Notable differences with respect to the wood particle source and decay fungi were also observed. Structural characterization confirmed the decay pattern of the fungi such as void cavities close the surface and the deposition of calcium oxalates.

Evaluation of zeolite catalysts on product distribution and synergy during wood-plastic composite catalytic pyrolysis

The catalytic pyrolysis of poplar wood-polypropylene composite (WPP) over different zeolite catalysts (HZSM-5, HBeta, HY, and HUSY) was investigated to obtain the influence of zeolite properties on both product distribution and synergistic effect using Py-GC/MS. The yield of aromatics was in the order: HZSM-5 > HY > HBeta > HUSY. HZSM-5 facilitated the formation of monomethyl aromatics, whereas HBeta and HY tended to promote the formation of polymethyl aromatics due to the larger pore size. The coke yield of HZSM-5 (6.4%) was much lower than those of other zeolites tested (11.4–20.2%), suggesting that the pore size of a zeolite was mainly responsible for coke formation during WPP pyrolysis. The strong synergistic effects between poplar and polypropylene in WPP pyrolysis were observed with all the zeolite catalysts tested as the experimental and calculated product distribution was significantly different. The synergistic effect over HZSM-5 zeolite promoted the selectivity for polyaromatics instead of mono aromatics, whereas the mono aromatics yield was increased by 28% for HBeta and 15% for HY zeolite. Our findings suggest that the catalytic pyrolysis of wood-plastic composites over the zeolite catalyst with suitable pore size and acidity might provide a viable and efficient route to generate hydrocarbons.

Comparative study of thermal degradation and flame retardancy between straw flour and wood flour on wood–polypropylene composites

The main aim of this study was to evaluate the thermal degradation and flame retardancy of straw flour (SF)-polypropylene (PP) composites and wood flour (WF)-PP composites. Biomass silica exists in SF, despite only 18 wt% loading of ammonium polyphosphate (APP); the APP in combination with biomass silica can effectively improve the flame retardancy on total heat release, heat release rate (HRR), mass loss rate, time to ignition (TTI), and limited oxygen index; it can obtain UL-94 V-0 rating, reduce the average and peak HRR by 44% and 41%, respectively, and increase the TTI by 8%. It attributes to the interaction effect between biomass silica in SF and APP, which more effectively enhances the thermal stability of the SF/PP/APP composites at high temperature and increases the char residue. The silica could form an intercalated network in char structure and then boost the physical integrity. The enhanced physical integrity and thermal stability lead to an effectively synergetic effect on flame retardancy of SF/PP/APP composites.

Mechanical, thermal and morphological properties of heat-treated wood-polypropylene composites and comparison of the composites with PROMETHEE method

ABSTRACTThe aim of the paper was to determine the mechanical, thermal, and morphological properties of heat-treated wood-polypropylene polymer composites (WPCs) and to select the composites having the optimum properties with the PROMETHEE method. In this study, polypropylene (PP) as a matrix, wood thermally treated at 180°C and 220°C as reinforcement filler were examined for preparing composites. The PP composites were compounded using a twin-screw extruder and test specimens were prepared by compression moulding. According to the test results, the thermal and mechanical properties of the WPCs generally increased with the addition of heat-treated wood fillers. The SEM images showed that the wood fillers dispersed better in the PP matrix as the particle size decreased from 40 mesh to 100 mesh. The WPCs having the optimum mechanical and thermal properties were determined for 40 mesh heat-treated wood at 220°C and 20 wt-% loadings with PROMETHEE method.

Effects of wood fiber properties on mold resistance of wood polypropylene composites

This study investigated the effects of mold susceptibility, total soluble sugar contents and chemical components of wood fibers on mold resistance of wood-polypropylene composites (WPC) filled with white poplar, moso-bamboo, Chinese fir, Ramin, white pine, red gum, red cedar, and rubberwood. Susceptibilities and resistances to molds were studied by artificially accelerated tests. The total soluble sugar contents and chemical components of wood fibers were analyzed by anthrone colorimetry and gas chromatography-mass spectrometry (GC-MS), respectively. Experimental results showed that the mold resistance of WPC varied significantly with wood fiber species. Higher natural durability of wood fiber resulted in higher mold resistance of WPC, while higher sugar contents decreased the resistance of WPC against molds. Low initial moisture content did not have any influence on the susceptibility of WPC towards fungal attack, but higher final moisture content was the result of heavy mold growth on WPC. GC-MS analysis suggested that different chemical components of wood fiber species affected the mold resistance of WPC either positively or negatively. This study provides an alternative solution to improve the durability of WPC against fungal attack.