The rheological modification of talc‐filled polypropylene by epoxy‐polyester hybrid resin and its effect on morphology,crystallinity, and mechanical properties

Reactive mixing of polypropylene (PP) and talc with epoxy‐polyester resin was preformed using a corotating twin screw extruder, and the rheology, morphology, crystallization behavior, and mechanical properties of composites were evaluated. The melts of composites mixed with resin exhibited yield stress and the variation of viscosity against frequency can be approximated in two lines with various slopes. The measurement of the suspension viscosity can be used to characterize the microstructural state of dispersion. Empirical formula was used to relate viscosity with particle concentration, and the analysis showed that the maximum volume fraction increases by using small amount of epoxy resin in the formulations. The morphological study of composites by scanning electron microscopy revealed that the use of resin improved the dispersion of talc in PP, which leads to the arrangement of talc platelets in the direction of flow even close to wall of the mold. The differential scanning calorimetry showed that the epoxy resin suppressed the nucleation effect of talc on PP while the degree and rate of crystallization increased. The compatibilization by maleic anhydride‐grafted polypropylene showed a noticeable increase in tensile strength of composites reactively mixed with epoxy resin. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Effects of lubricants on the rheological and mechanical properties of wood flour/polypropylene composites

The lubricant is an indispensable agent used in wood plastic composites (WPCs) to improve the processing flowability, especially with high wood content. Here, the effects of different lubricating systems on the rheological and mechanical properties of wood flour/polypropylene (WF/PP) composites are investigated. Additionally, several theoretical models are used to describe the rheological behavior. The results show that stearic acid (SA), semirefined paraffin wax (Wax), and zinc stearate (ZnSt) can decrease the equilibrium torque, complex viscosity, relaxation time, and flow activation energy of the composite melts. Compared to a single lubricant, the combination of Wax and SA lubricants exhibits lower values and the composite with 3 wt % SA and 1 wt % Wax has the best lubricating effect. The synergistic effect of the combined SA and Wax lubricants further decreases the interactive force between the molecules, indicating that multifunctional lubricating systems play a predominant role in WPCs and improve the overall processing properties. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47667.     

Investigation on the dynamic melt rheological properties of polypropylene/wood flour composites

The rheological behavior of polypropylene/wood flour (WF) composite was investigated at constant temperature over a wide range of frequencies using a mechanical compact rheometer operated in the dynamic mode. The effect of WF content, particle size, and coupling agent on melt rheological properties were investigated. The melt rheological data in terms of complex viscosity (η*), storage modulus (G′), loss modulus (G″), and loss tangent (tan δ) were studied and compared for different samples. It was found that complex viscosity increases with increasing wood content and coupling agent. Compatibilization using coupling agent increased both storage modulus and loss modulus, but the variation of storage modulus is more. By increasing wood content storage modulus increases. Complex viscosity, storage modulus, and loss modulus showed a minimum value by increasing of wood particle size. Tan δ decreases with increasing of wood content. Cole–Cole plot indicated that relaxation process changes with addition WF, coupling agent, and using different mesh size of wood. The Han plots revealed the sensitivity of rheological properties with composition at constant temperature. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Tensile properties of wood flour/kenaf fiber polypropylene hybrid composites

Hybrid composites of wood flour/kenaf fiber and polypropylene were prepared at a fixed fiber to plastic ratio of 40 : 60 and variable ratios of the two reinforcements namely 40 : 0, 30 : 10, 20 : 20, 10 : 30, and 0 : 40 by weight. Polypropylene was used as the polymer matrix, and 40–80 mesh kenaf fiber and 60–100 mesh wood flour were used as the fiber and the particulate reinforcement, respectively. Maleic anhydride and dicumyl peroxide were also used as the coupling agent and initiator, respectively. Mixing process was carried out in an internal mixer at 180°C at 60 rpm. ASTM D 638 Type I tensile specimens of the composites were produced by injection molding. Static tensile tests were performed to study the mechanical behavior of the hybrid composites. The hybrid effect on the elastic modulus of the composites was also investigated using the rule of hybrid mixtures and Halpin–Tsai equations. The relationship between experimental and predicted values was evaluated and accuracy estimation of the models was performed. The results indicated that while nonhybrid composites of kenaf fiber and wood flour exhibited the highest and lowest modulus values respectively, the moduli of hybrid composites were closely related to the fiber to particle ratio of the reinforcements. Rule of hybrid mixtures equation was able to predict the elastic modulus of the composites better than Halpin–Tsai equation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Water absorption and mechanical properties of PP/HIPS hybrid composites filled with wood flour

Water absorption and mechanical performance of the injection‐molded hybrid composites prepared from different ratios of two polymer blends (57 wt%), two compatibilizers (3 wt%), and two wood species (40 wt%) were investigated. The ratio of polypropylene and high‐impact polystyrene (HIPS) gradually increased in the blend (from 10 to 30 wt%). Styrene–ethylene–butylene–styreneblock copolymer and maleic anhydride‐grafted PP (MAPP) were used as compatibilizer (3 wt%). The shore D hardness of the PP/wood composites was improved by the incorporation of the HIPS. The HIPS/wood flour composites showed higher tensile modulus but lower tensile strength than the PP/wood composites. The water resistance of the PP/wood composites decreased with increasing HIPS content. POLYM. COMPOS., 38:863–869, 2017. © 2015 Society of Plastics Engineers     

Moisture absorption effects on the thermal and mechanical properties of wood flour/linseed oil resin composites

The thermal and mechanical behavior of new natural polymeric composite materials after exposure to humid environments must be well known and understood in order to predict their performance in final applications. For this reason, composites made from unsaturated polyesters based on linseed oil and filled with wood flour were exposed to environments of different relative humidities and their final properties were measured. In general, the equilibrium moisture content increased as the wood flour percentage increased. Dynamic mechanical tests performed in temperature scan mode were carried out in order to monitor the changes resulting from moisture absorption on the main transition temperature of the matrix (T_α). The temperature of this transition decreased as the amount of absorbed water increased, but the effect was partially reversible by re‐drying the samples. The mechanical properties were also strongly affected by moisture. The flexural modulus and ultimate stress of the composites decreased after equilibration in humid environments. Copyright © 2006 Society of Chemical Industry     

Thermal and mechanical properties of polypropylene/wood‐flour composites

In this research, polypropylene/wood‐flour composites (WPCs) were blended with different contents of wood and/or maleated polypropylene (MAPP) and clay. We found that the addition of MAPP or clay in the formulation greatly improved the dispersion of the wood fibers in the composite; this suggested that MAPP or clay may have played the role of an adhesion promoter in the WPCs. The results obtained with clay indicate that it also acted as a flame retardant. The thermal tests carried out with the produced samples showed an increased crystallization temperature (T_c), crystallinity, and melting temperature (T_m) with wood loading. The increase of the two former parameters was explained by the incorporation of wood flour, which played the role of nucleating agent and induced the crystallization of the matrix polymer. On the other hand, the T_m increase was ascribed to the insulating properties of wood, which hindered the movement of heat conduction. The effects of UV irradiation on T_m and T_c were also examined. T_c increased with UV exposure time; this implied that UV degradation generated short chains with low molecular weight that could move easily in the bulk of the sample and, thus, catalyze early crystallization. The flexural strength and modulus increased with increasing wood‐flour content. In contrast, the impact strength and tensile strength and strain decreased with increasing wood‐flour content. All of these changes were related to the level of dispersion of the wood flour in the polymeric matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Investigation of the dynamic mechanical behavior of polypropylene/(wood flour)/(kenaf fiber) hybrid composites

Polypropylene/(wood flour)/(kenaf fiber) hybrid composites were prepared in an internal mixer. Kenaf was considered as a fibrous filler and wood flour as a particulate filler. The lignocellulosic loading used was 50%. Dynamic mechanical thermal analysis properties such as storage modulus (E′), loss modulus (E″), damping factor (tan δ), and adhesion factor were evaluated. It was found that the adhesion factor could interpret the interfacial adhesion between lignocellulosic fillers and the plastic matrix macroscopically. This factor was affected by the type of filler used and the coupling agent concentration. The variation of storage modulus was affected more by the shape of the filler and the coupling agent concentration at higher temperatures than at temperatures below the glass transition. Owing to a higher probability of agglomeration in a sample containing 50 wt% of wood flour, the storage modulus and complex viscosity of this sample were higher than those of other samples. Cole‐Cole diagrams showed that the homogeneity of samples containing a higher amount of coupling agent was higher than that of samples with a lower concentration. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

Melt rheological properties of polypropylene–wood flour composites

This article presents study of melt rheological properties of composites of polypropylene (i-PP) filled with wood flour (WF), at filler concentrations of 3–20 wt%. Results illustrate the effects of (i) filler concentration and (ii) shear stress or shear rates on melt viscosity and melt elasticity properties of the composites. Incorporation of WF into i-PP results in an increase of its melt viscosity and a decrease of melt elasticity such as die swell and first normal stress differences; these properties, however, depend on filler concentration. Processing temperature of the filled i-PP increases as compared to the nonfilled polymer.     

Modified polypropylene wood flour composites. II. Fracture,deformation, and mechanical properties

The effect of grafting level of maleic anhydride (MA) in the maleated polypropylene (PPMA) on the fracture, deformation mechanisms, and mechanical properties of polypropylene (PP) wood flour composites was studied. Tensile strength, elongation at break, and impact strength are noticeably improved with addition of interfacial modifiers as maximum values of the examined mechanical properties were detected when concentration of MA in the compatibilizer was 1 wt %. To explore the microstructure and deformation mechanisms, scanning electron microscopy was employed. It was found that low concentrations of MA up to 1 wt % led to the creation of a thin and irregular polymer layer assisted formation of fibrillated plastic deformation zone around the wood particles, while the bulk PP matrix experienced voiding and brittle fracture. Higher concentrations of MA fetch to stronger interaction between PP and wood flour, the reason for brittle fracture and reduced ductility of the matrix. The impact fracture behavior of the composites during Instrumented impact tests is also discussed with respect to the interfacial bond strength. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1286–1292, 2004     

Flammability and mechanical properties of wood flour‐filled polypropylene composites

Polypropylene (PP) composites filled with wood flour (WF) were prepared with a twin‐screw extruder and an injection‐molding machine. Three types of ecologically friendly flame retardants (FRs) based on ammonium polyphosphate were used to improve the FR properties of the composites. The flame retardancy of the PP/WF composites was characterized with thermogravimetric analysis (TGA), vertical burn testing (UL94‐V), and limiting oxygen index (LOI) measurements. The TGA data showed that all three types of FRs could enhance the thermal stability of the PP/WF/FR systems at high temperatures and effectively increase the char residue formation. The FRs could effectively reduce the flammability of the PP/WF/FR composites by achieving V‐0 UL94‐V classification. The increased LOI also showed that the flammability of the PP/WF/FR composites was reduced with the addition of FRs. The mechanical property study revealed that, with the incorporation of FRs, the tensile strength and flexural strength were decreased, but the tensile and flexural moduli were increased in all cases. The presence of maleic anhydride grafted polypropylene (MAPP) resulted in an improvement of the filler–matrix bonding between the WF/intumescent FR and PP, and this consequently enhanced the overall mechanical properties of the composites. Morphological studies carried out with scanning electron microscopy revealed clear evidence that the adhesion at the interfacial region was enhanced with the addition of MAPP to the PP/WF/FR composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The effect of filler content and size on the mechanical properties of polypropylene/oil palm wood flour composites

The effect of filler content and size on the mechanical properties of a new type of wood-based filler, oil palm wood flour (OPWF), in polypropylene (PP) was investigated. Four sizes of OPWF filler at different filler loadings were compounded using a twin screw compounder. All sizes of filler showed a similar trend of declining mechanical properties with increasing filler content. In terms of size, the composites filled with larger-sized filler showed higher modulus, tensile and impact strengths, particularly at high filler loadings. The OPWF used in this study was not treated with any coupling agent.     

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     

Silica‐filled polypropylene composites: The effect of ethylene diamine dilaurate and maleic anhydride grafted polypropylene on mechanical properties,water absorption,morphology, and thermal properties

The effect of two compatibilizers, i.e. ethylene diamine dilaurate (EDD) and maleic anhydride grafted polypropylene (MAPP) on the mechanical properties, water absorption, morphology, and thermal properties of silica‐filled polypropylene (PP/Sil) composites were studied. The results show that the tensile, impact and flexural strengths (up to 2 php), Young's modulus, and elongation at break (Eb) increased with increasing EDD content. However, increasing MAPP content increases the tensile strength, Young's modulus, impact and flexural strengths, and water absorption resistance. At a similar compatibilizer content, EDD exhibits higher Eb, impact and flexural strengths but lowers tensile strength, Young's modulus, and water absorption resistance compared with MAPP. Scanning electron microscopy study of tensile fractured surfaces exhibits the evidence of better silica‐PP adhesion with MAPP and EDD compared with the similar composites but without compatibilizer. Fourier transform infra red spectra provide an evidence of interaction between EDD or MAPP with PP/Sil composites. Termogravimetry analysis results indicate that the addition of EDD or MAPP slightly increases the thermal stability of PP/Sil composites. Differential scanning calorimetry also indicates that PP/Sil composites with EDD or MAPP have higher heat fusion (ΔH_f(com)) and crystallinity (X_com) than similar composites but without compatibilizer. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

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

The 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     

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     

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     

The effect of dynamic vulcanization on mechanical properties and water absorption of silica and rubberwood filled polypropylene/natural rubber hybrid composites

Dynamic vulcanized silica and rubberwood filled polypropylene (PP)/natural rubber (NR) hybrid composites were prepared using a Brabender plasticorder at 150°C and a rotor speed of 50 rpm for 12 minutes. The effectiveness of the dynamic vulcanization was indicated by the Brabender plastograms. The mechanical and water absorption properties of hybrid composites with different concentration of sulfur were investigated. Significant enhancement in mechanical properties, viz. tensile strength, stress at peak, Young modulus and flexural modulus were observed for dynamically vulcanized hybrid composites compared to unvulcanized hybrid composites. This has been attributed to the increase in crosslink density, which was manifested by a reduction of water absorption and increase of stabilization torque at the end of mixing stage with increasing sulfur concentration.     

Static and dynamic mechanical properties of a kenaf fiber–wood flour/polypropylene hybrid composite

A natural fiber hybrid composite containing equal proportions of kenaf fibers (KFs) and wood flour (WF) as the reinforcements and polypropylene (PP) as the polymer matrix was prepared, and its static and dynamic mechanical properties were compared with KF/PP and WF/PP composites. Static tensile and flexural tests and dynamic mechanical analysis (DMA) were carried out. The hybrid composite exhibited tensile and flexural moduli and strength values closer to those of the KF composite, which indicated a higher reinforcing efficiency of KFs compared with WF. DMA revealed that although the glass‐transition temperature remained unchanged by the replacement of half of the WF by KFs, the α‐transition temperature of the hybrid composite was identical to that of WF composite. The magnitudes of both the α and β (glass) transitions of the hybrid composite were comparable to that of the WF/PP composite. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 665–672, 2005